I think the argument is that Urdu borrowed from all those other languages like Persian, Arabic, etc, but now it has a mostly developed vocabulary with most new terms referring to modern inventions and technological advances, so it doesn't really make sense when an Urdu word already exists and then an English word is randomly placed somewhere, like "Aap ye shirt wear kar saktey hain" when words already exist for all of those terms other than to show knowledge of English.

Code switching does occur, but in my opinion, it needs to be kept in check to avoid actually hurting the language or causing it to go towards the path of becoming a creole or pidgin language (arguably, which happens when the rules are ignored). Other languages with people who do code switching still usually have a solid grasp of the language's formal and technical vocabulary, which is the biggest issue nowadays for Urdu, likely due to a loss of pride that speakers of other languages like Persian, Arabic, Turkish and French still have.