Probably because their president isn't on tv endorsing those horrors, funding them with their tax dollars and in general having their mainstream media champion them.
I'm not sure if those teens even know how to spell Yemen.
First, it's factually inapposite, because we don't have a bunch of disproportionately pro-Saudi American companies and billionaires trying to intimidate people speaking in favor of Yemeni civilians, considering ad blitzes to gaslight and obfuscate the issues, etc. We don't have a significant pro-Saudi bias in the media such that it views the conflict there as worthy of constant reporting and also as a relatively black-and-white struggle where Yemeni civilians either are getting what they deserve or are merely unfortunate collateral damage for justifiable military actions. We don't have a strong contingency of people in this country trying to act like speaking out against the killing of Yemeni civilians is being "pro-terrorist".
Second, it's logically inane to say that someone's criticism of something is invalid because they didn't speak out or criticize some other thing that they most likely don't even know about.
And nothing I pointed out about how differently the war in Yemen is situated in the Western consciousness (i.e. basically not at all) versus this one matters?
I believe that most American teens opinions on this matter are influenced by either anti-Islam or anti-Jewish messaging they read through social media, and not a genuine interest in the conflict.
I'm not saying the criticism of Hamas and/or Israel is invalid, I just found it worth pointing out that there are conflicts that teens somehow can make up their mind on (that's TikTok's claim, not mine) and strong enough that they take to the streets for that, while they likely haven't heard of other somewhat comparable conflicts (support by "their government", civilians dying, half the world away, ...) at all.
Maybe it's just the general media circus (Yemen _isn't_ very present in the media, after all), but "algorithm" or not, I'm considering TikTok part of that media circus.
As such, "the kids are just voicing their opinion" seems a rather shallow excuse to me: They pick up what gets amplified. Having no idea about Yemen but strong opinions on "who's the baddie" in Gaza (since folks like to talk colonialism: it's clearly the UK) doesn't sound like an independently formed opinion at all, and so I'm not willing to let TikTok (et al) off the hook.
Even if we take what you’re saying at face value, the notion that you can’t speak out about something that is wrong because there are other things that are also bad is preposterous.
We are talking about teens here, you basically chastising children for not taking to the streets when they were 10 years old, when the Yemen conflict started.