Why build one hammer and use it forever when you could pay $100 a month to build a new hammer every time you need to hit a nail?
for the database it is actually the opposite, as it is a swiss army knife.
look at the sibling comment, people are already doing this. with time only more people will.
an era is ending. there is a time and a season for everything.
Databases, like filesystems, are one of those pieces of infrastructure you do not want to build yourself unless you have a really good reason. They're complex, and you will not catch all the bugs yourself.