Bitcoin is still the base of all alts . To buy alts you need to buy bitcoin first ,thus it will never unpopular or irrelevant .
Yes other coins might make you more profits but i think of bitcoin as storing value that in the long run gonna make me profits on my assets too.
Bitcoin price might dump drastically if more alts became paired with other coins and there was no need to buy bitcoin first to buy alts.
i buy my alts using eth so basically i dont need btc rn but that dont make it useless or unpopular because it has many advantage than other crypto coins like you can buy real stuff using btc and that is something important while using other alts will not allow you to do the same
and like ppl said alt are simply alternative to btc all what i see is people making profit with alts and gaining more btc . so the whole game is about making more btc when you use alts ,also lot of alts fail in the long run and that make it harder for them while btc did well in the long term so people may have more trust on it as a safe of value while alt as a temporary way to gain more btc