God's Israel holds the ancient feasts to this day, if you ever bothered to look some calendars.
But, of course, you only care about how the anti-Christian sect of Jews performed feasts after the destruction of the temple.
There were Jewish Christians who followed the Law and were Orthodox. Then there were neoplatonist fringe Jewish Christians who did a bunch of wacky stuff. And there were also Christians who joined in the versions of feasts practiced by the anti-Christian sect, and these were reprimanded.
Your understanding of Judaism is that Rabbinic Judaism is real Judaism and Christianity is some non-Jewish thing. Have you, then, never really read St. Paul? Romans 9?