Essentially, two diverse approving bodies means every law change goes slower. Slower law change gives everyone else a break during the (at least) 50% of the time that the lawmakers are assholes or idiots.
Getting rid of US bicameral legislature will be a weird process, because actively adding a new, better, but still slow-by-design governing body is likely a hard topic to get wide agreement on.
Also there’s currently a lot of old rich white men in the senate who probably want their kids and their grandkids to take over their Senate seats. That’ll likely be a struggle, itself.