They do exist, from memory they have another type of bacteria instead and there’s even a project trying to transfer it from people with it to people without it.
Also as you said evolution doesn’t try to fix stuff and there’s a whole lot of stuff that could have evolved for the better (heck, we’re not even that well adapted to be standing up!), but if it doesn’t prevent reproduction then it gets passed down.
If I remember this study it required a formulated liquid for “feeding” the good bacteria that kept away the bad bacteria. Not sure what came of it.
Edit: not the same. Getting my studies mixed up. This is the one I was thinking of, it’s a mouthwash to get rid of destructive bacteria.
The one I’m thinking about was in trial in a bio engineering community somewhere in Latin America (easy way to get financing, get people to pay to be your guinea pig)
Found it!