People are randomly arrested and detained base on official government policy. And they have been arresting and detaining people long before Jan 2024, but it was scaled up recently. A recent story made it clear that some people with minor visa overstays have already been detained for months: https://news.ycombinator.com/item?id=43410548

The fact is if you care about people from all around the world being able to attend your conference, the U.S. hasn’t been a good location for a long time. That’s not new. In fact [2][3] is only noteworthy because it was an influential individual (in this circle) with a strong passport; people with weaker passports are routinely denied. Hell sometimes UN diplomats are denied.