As a former Southern Baptist, my short answer to your question is this: It is because of demons and disbelief.
Here is the long answer. Some of these deceived pastors you refer to are very sincere in their faith but have been mislead by demons. Others, however, are probably insincere. They are hypocrites who are in it for the money. There is probably a mix of people who are half sincere but half in it for the money. Israeli politicians also probably foster this. They probably pay for these men to come take grand vacations in "the holy land" and fill their pockets with all sorts of things while telling them what to tell their congregations about the nation of Israel. This sort of thing goes on all the time in our government. The majority of our Congress has been brought to Israel for free tours, and they've been politically indoctrinated while there. This probably happens with many Protestant churches too. Israel's political leaders are not stupid. They know that the churches in America are the root of the political power in America.
Step aside with me for just a moment from the topic of Israel to the topic of demons. The teachers who emphasize a need to support the modern state of Israel are often the same teachers that
1) forbid or hinder alcohol use (despite the many passages in holy Scripture that say alcohol is blessing in moderation),
2) forbid or hinder cannabis use (despite Genesis 1, "all seed bearing plants" are for all men to consume in moderation if they they want),
3) forbid or hinder the use of sexual passion for the formation of marriage (despite the fact that reading Song of Solomon twice will teach you in no uncertain terms that sexual passion is part of what forms holy marriage; when you forbid sexual passion prior to marriage and you are hindering marriage itself).
Basically, they fit perfectly into the prophecy given in 1st Timothy chapter 4.
The Spirit clearly says that in later times some will abandon the faith and follow deceiving spirits and things taught by demons. Such teachings come through hypocritical liars, whose consciences have been seared as with a hot iron. They hinder the formation of marriages and order people to abstain from certain foods, which God created to be received with thanksgiving by those who believe and who know the truth.
The main point I'm trying to make is this: Demons are trying to influence our behavior by influencing our thoughts not just about the things in 1 Timothy 4, but about everything. Many of us, and especially many of our church leaders (even in orthodoxy but especially outside of orthodoxy), are following those demons in one way or another. The Elder Thaddeus of Vitovnica rightly taught that "most of the thoughts which torment us from the inside are not ours at all; they come from the demons." (quote from Our Thoughts Determine Our Lives, the life and teachings of Elder Thaddeus of Vitovnica, page 48, printed by the St. Herman of Alaska Brotherhood in 2011)
Although these "pro-Israel" pastors you mention may think their teachings come from God through their own rational observations and thoughts about Him, they don't. They probably often come from Israeli politicians also from demons. Israel's political leaders have accomplished a lot of evil in this world. I'm not trying to say I'm better than them. I'm the chief among sinners. But I do honestly suspect the goal of many leaders in Israel is to take over America from the inside out in order to accomplish their own selfish desires. They are not our allies; they pretend to be. If you've never looked up the U.S.S. Liberty Incident (when Israel attempted to destroy a U.S. military ship, murder its crew, and leave no evidence)... do it. Read about it, and especially read the first hand accounts and explanations written by the U.S. sailors involved and their loved ones. That was no mistake. Israel's military leadership knew exactly what they were doing as is obvious from a detailed examination of the facts. Israel's military apparatus has been caught stealing from America too many times to count in various "spy" cases. Also investigate the facts surrounding the "dancing Israelis" (the group of Israeli Mossad agents that filmed the 9/11 attacks in New York city while dancing and shouting for joy). Their leaders own many of our politicians, and I wouldn't be surprised if they own many of our church leaders also.
That's politics. As far as spirituality, even if corrupt people don't "own" these Protestant leaders you refer to in the sense that a bribed politician is "owned," I think the same demons own their minds. Scripture says Satan masquerades as an angel of light, and many of these church leaders would probably tell you that "God" has told them to support the modern political state of Israel. "God" is not the one telling them to rely on misunderstandings of old testament passages about Israel. The holy Apostle Paul clearly taught that Israel has been "broken off" from God and the gentiles have been "grafted in" in their place. But many of these pastors refuse to believe the Word of the True God. With the help of demons who pretend to be God, many of these men ignore the Apostolic teachings about Israel. Their own sinful desires probably also push them down the wrong path. In the same manner that Israel wanted a physical king, these men probably want to be able to see a physical "nation of God." Therefore, they are easily deceived into thinking modern Israel is it.
However, the truth is this: Jesus Christ is the new Moses, old Israel is the new Gentile, and the Church is the new Israel. No Christian has any duty to support any political, national entity that calls itself Israel, and no American has any duty to support the atrocities that Israel's military commits. However, many Americans have been thoroughly deceived on both of those points.
We, Americans, have been deceived by demons and by corrupt men.
I hate to generalize, so everything I say here is based off of my own personal experience. So, I am asking, why do so many modern Protestants in America support Israel so much? ...