I understand that every shitcoin = altcoin = eth
You've understood it wrong.
There is indeed Bitcoin and altcoins. And tokens too. But, although some maximalists have a way too narrow opinion which you also were unlucky to see, no, not all altcoins are shitcoins. A tiny minority is good coins.
But why eth sill doesn't have a separate category.
Because this is still
Bitcoin talk, hence ethereum is part of "the others".
And although ethereum has value (possibly historical though), I think it's now overrated.