But there is evolutionary pressure to lose traits over time. Loss of traits over time is fundamental in evolution. Resistance carries fitness and metabolic cost

But there is evolutionary pressure to lose traits over time. Loss of traits over time is fundamental in evolution. Resistance carries fitness and metabolic costs and evolution is always looking to squeeze out certain traits if they're no longer integral to survival. Moles losing eyesight, flightless birds losing fight musculature and hollow bones once they shifted to new strategies, humans losing the ability to synthesize our own vitamin C when we could get it from a diversified diet. There's also now strong documented history of bacteria losing resistances over time hence the rotating strategy. Granted, some resistances are "cheap" to maintain and not lost, or recirculated in the wild and it's not a panacaea (it's more a hypothesized strategy than a realized one and it hasn't solved the issue), but it's by no means a failure to understand evolutionary principles.