Several databases index everything, needed or not. (And sometimes have mechanisms to force it off for some specific data)

Even this isn't sufficient, because some problems with over-indexing don't become apparent until the size of a table gets much larger, which only happens a drop at a time. I suppose if it was always probationary and continually being evaluated, at some point it could recognize that for example INSERTs are now taking 1000x longer than they were 2 years ago. But that feels like a never-ending battle against corner cases, and any automatic actions it takes add significant complexity to the person debugging later.