Perhaps one reason for the protest is that the US is fully supporting and arming the country killing the civilians—yes, there are a lot of civilians being killed there—whereas in the case of Ukraine the US is actively arming the resistance against the aggressor, so there’s no need for the kids to protest the government’s and university's actions on that one.
I also believe the vast majority of protesters are anti-bombing and anti-supporting the country doing the bombing only, and only a small sliver are actually anti-Semitic or pro-Hamas, and the latter is all anyone in the press wants to report on, because it’s sexy news. Some people might counter that anyone participating in any protest is automatically pro-Hamas. I would strongly disagree with such a counter.
As to why it started spreading all of a sudden last week, I believe that was a reaction to police crackdowns on students at campuses all across the country, especially in Texas, where the governor said in practically so many words that he sent troops not because they’re being violent or anything like that, but because he doesn’t like what side of the issue they’re on and that these protesters belong in jail full stop.
As for Roe, I seem to remember there were a lot of protests on campus for that one, unless you have info to the contrary? As for guns and school shootings, if US policy had changed and there were a sudden surge in school shootings from almost nothing to being everywhere as a result, I’d think they’d be protesting that en masse. Instead, mass shootings is more of a slow burn issue occurring over decades than an immediate fireball issue occurring across the space of months.