Big alts are buying bitcoin and using it as collateral, or wrapping it, or using it as part of their defi shenanigans.
Alts used to exist independently to compete with bitcoin, now they're drag it along with them and screwing bitcoiners.
They understand as well that they have no good standings as bitcoin has and needed it support to have a strong backbone for their existence, if truly those alts coins were really of a standard worth Valued to that of bitcoin then they wouldn't have been seeking for supportive backup from bitcoin, imagine if where you are running to for help is still soliciting help elsewhere too, same is what's going onbwith altscoin vs bitcoin.