Protestants are a different story. The idea of sacred space is generally absent in Protestantism. In Geneva, John Calvin told everyone to lock the church doors outside of regular services to discourage it. You can pray anywhere, so why do you need to come to some special place to do it? Must be idolatrous. Better lock the doors.
That explains why the buildings are not open for informal prayer - they intentionally blocked it at a root period of their history.
Still, why not have daily community prayers, even if only a fraction of the people come, like 10 people?
As for the Catholics, 22% is a huge minority, especially considering that Orthodox are less than 1%. Also, Catholics are often concentrated in particular areas. For instance, in Philly and surrounding suburbs the Irish, Italian, Polish, and Latino populations.
22% is a huge minority, but remember that there are places in the US where they are much smaller than that, because like you said they are concentrated in certain areas. And in those smaller places, I expect that their population can be less than Orthodox churches covering larger populations in the US. So for example, I know two Malankaran Indian Orthodox churches who cover 2000 people (actually listed as parishioners) and they have liturgy only twice or thrice a week. And there are Greek Churches in the big cities with even bigger coverages.
Meanwhile, like I said, you can expect the RC churches to have daily prayer services or more often mass. But the Orthodox and Protestant ones will only have services about twice a week even if they cover more people.
One or more Orthodox cathedrals or big churches in the biggest US cities will have very large congregations with volunteers and with paid staff. One I know has a security guard, secretar(y/ies) and pianist. Such big Orthodox churches can have a paid deacon(s) too. And yet this massive Greek Church has only one liturgy / prayer service for the whole week, on Sunday.
That seems to be pretty normal in GOARCH. I wouldn't say that this represents something that be generalized across the Orthodox world.
You are right.
So why don't big GOARCH churches who meet these descriptions have daily services?
Also, however large the congregation might be, they may be rather scattered. If it's not in a predominately Greek or Orthodox neighborhood it's unlikely that people will stop by at odd hours to pray.
I mean, does having a married or unmarried priest make that extreme a difference? There are some Orthodox and Protestant churches where for whatever reason the priest does not have a wife.
Raising kids is a full-time job, even if most people are forced by economic necessity to behave otherwise.
Granted, there are many cases where Orthodox churches can and should have more services, more open hours, etc.
If we asked Greek and Russian churches why they don't, many would give the reasons you did, along with correctly saying that the place could get robbed or that no one would come. If you are talking about your standard EO church with maybe 60-300 parishioners, that's true.
However, there are big coal towns you must know (I can name some) that are mostly (70%?) Catholic, with big representations of Poles. Poles are the largest group in Luzerne County. And there are lots of Ukrainians in coal towns, with Ukrainian Catholic churches being the size of Orthodox cathedrals and looking like they belong in a major city. And yet the Eastern Catholics won't have daily mass, but RC churches in these medium-big towns and small cities will.
There are small coal towns and city neighborhoods that have been mostly a mix of Eastern Catholics and Orthodox for 90 years, and I doubt they had daily mass even when they were booming. The neighborhood/town of Duquesne and its nearby surrounding area outside Pittsburgh has had 3-4 Eastern churches, and the Byzantine church there had a 6 PM service the day I stopped by (a Saturday?).