I don't understand it.
There are places like Albufeira, which I've never visited, but I understand to be the archetypal tourist place - but apparently still has proper Portuguese areas - so why don't they just go there?!
And Carvoeiro, still no doubt beautiful but even 30 years ago was getting way too touristy for me.
In Spain, here, you hear of Torremolinos and most people would think 'Blackpool with sun' but actually, it's not like that - unless you want it to be, in which case you can seek out those bars, etc.
As with everywhere, there will always be those Brits that behave like the worst example of brits, but there are also plenty that are not at all like that - but much less noticeable.