Most mammals instead evolved to have their teeth keep growing, like beavers, thus they need to keep using their teeth to keep them from growing out of control.
Secondly, humans in particular, added tooth-enamel-eating-bacteria into our diet hundreds of thousands of years ago. Before that, we didn’t have a huge number of issues with our teeth, and so perhaps not enough time has actually passed since we got the bacteria eats our teeth for an evolutionary advantage that stops it from being an issue? Evolution isn’t so cut and dry, it’s not like it’s trying to solve problems. People with resistances to mouth bacteria probably exist, but are they reproducing enough to become the dominant geneaology? Who the fuck knows?