If we eliminated treatment with drugs with resistances against them, we'd no longer be artificially selecting for those bacteria, which would mean the bacteria that naturally performed better would be the most likely to survive.

Essentially if we stop treating with the drugs with resistances against them, we'd eventually end up with a bacteria gene pool that resembled the original pre-resistant one, where resistant bacteria were replication errors that were drowned out by natural selection.

The only issue is we can't do that without sacrificing millions of lives. So having a drug that works via completely different mechanisms would fulfil both.