We're at a point now where Lebanon is being subjected to israel's Gaza Doctrine, and it seems like most people don't know or don't care.

If not a complete disregard for humanity, is it boredom? It must be more than race-hatred. Does the death and suffering become too much for our brains to make sense of it, so we stop caring?

Had millions of people not been killed by COVID, would the world be less tolerant to genocide?

It's always been a thing to a greater or lesser extent; there's always a detachment to some degree to mass death/suffering abroad and there's levels of justification and excuses at every level of the chain. At the top it's that they genuinely don't give a shit about large numbers of poor people dying and even when they say they care (e.g. the Uyghur genocide allegations) they don't actually give a shit and it's purely for propaganda purposes. For the average soldier or worker invested in the military, it's "it's not my fault, my contribution is minimal, I'm just following orders from above, it's their fault for commanding me to do this." For the average citizen, the genocides only exist in their nightmare rectangles and they either excuse it ("Hamas shouldn't have provoked Israel, FAFO") or denounce it with necessarily pointless actions because useful ones will make you face consequences - sending money directly could get you investigated, public shows of support could get you fired or even a knock on your door from police.

So everybody's just trying to survive and forming justifications for their ideology after the fact. There's almost never an avenue to help a large group of people in very difficult situations that wouldn't a) bankrupt you and your family, b) take up a lot of time that you're too tired to spend because you're working, and/or c) make you face punishment, so what's left is stochastic violence (complete with a manifesto!) that achieves nothing, or extreme acts of individual protest like setting yourself on fire which also achieves nothing (in a vacuum; sometimes it can be effective if there's an organisation behind you to take advantage of the publicity). This is certainly amplified by the West's propaganda but propaganda doesn't work unless you have some other reason to believe it.

I wouldn't even call it "acceptance" - nobody would say that they "accept" that tons of people die from cancer every year. That's not to draw equivalency between relatively random biological phenomena and humans making a decision to drop bombs onto civilians, it's just that for the average person - even here in this thread! - we can no more miraculously cure a terminally ill person of cancer as stop a bomb from being dropped by an Israeli plane onto a school full of children. It all gets sorted into the same compartment of "terrible things that are happening reasonably far away from me". There is no democratic input into what is going on in Gaza or Lebanon. The only conceivable possibility would be Jill Stein winning, but everybody's too caught up in the prisoner's dilemma to shift their vote from the Democrats to her, and even if they did, Stein would get Kennedy'd by the feds before she could put her signature on the bill to stop weapon shipments to Israel. Inside Israel, there's literally nobody else to vote for, and the overwhelming majority of Israel is only angry at the current government because the genocide isn't happening fast enough and they're confused why there wasn't a dozen nukes dropped onto Gaza on October 8th - and also, of course, they're angry that they're facing consequences for their actions.

I do think that Westerners are uniquely selfish due to their material position over the rest of the world, but I don't think coronavirus had anything really to do with it. All it proved is that they're not even willing to do much of anything even if many of them die, but the "acceptance" - such that it is - of mass death is, in my opinion, a) a phenonemon which dates back centuries, and b) kinda neither here nor there, because Western societies are already profoundly undemocratic and are highly surveilled police states, so there's little opportunity for genuine, shaking-the-foundations revolutionary anger to go anywhere, as 2020's BLM protests and the Iraq War protests indicated. So sure, you could vote for XYZ candidates or join anti-Israel orgs, but until material conditions significantly change, it won't be allowed to influence policy significantly. There's millions dying abroad, that's what's given to you as a fait accompli - all the average Westerner can do is "decide" what emotional response they will have to that, and then go off and do the laundry and dishes and then go to work tomorrow.