RPGMemes

A significant part of the culture that has formed around 5e is about "having it all". And usually by ignoring the (admittedly weak) rules that do exist, rather than exploiting actual gaps. So, you can frankenstein together a caster that has martial proficiency in armour (or even melee weapons), with the only compromise being your capstone abilities (which often are very expendable). And then you can metagame away your shitty social abilities by "roleplaying".

I'm not going to defend 5e -- I genuinely think it's a poorly made game, and place the blame for that entirely on the execuitives -- but the reason why so many people refuse to try something else is because they like the exploits that they believe exist, even though they are totally socially constructed.