I know I'm part of it, everyone is who goes to a tourist or latest instagram spot and relatively few want to go off the beaten track. Those who do are generally young, fit, cycle or hike over mountains, wild camp or vanlife it, and so on to find that special little spot that is relatively inaccessible and undiscovered. That's fine, it brings in funds to that area I suppose, but not everyone can do that.
I try to go to places that do not have cruise ship docks, I check carefully. Rome is one that I couldn't escape but the dock is in Civitavecchia which is a good bit away from the city, and Rome is big so can absorb them, it will be jammed anyway, cruise ships or not!
To try and mitigate the effect of crowds (on me!) I never go away June - September, or at half terms and other school hols. Apart from anything else the heat is becoming impossible to deal with now, and add in crowds and it's just not enjoyable.
So my travelling is done October - May, and while there are still lots of people about (including me!), the frenzy and queues of the traditional holiday season is not there as much. I am not a sun lover and don't mind a bit of rain and a cold day so it works for me.