How the fuck did clients convince themselves they can have a developer build an Amazon, booking.com, Facebook, Airbnb or site of the sorts for 500 bucks on FUCKING WORDPRESS?!

Because they dont fucking know any better... and we just keep giving them this shit...

Because they're uninformed.

What do you expect? Sure, common sense for us and even slightly technological people says that's not gonna happen.

But when they're extremely uneducated, you can't exactly expect anything better.

Because there dicks!

Because there will be someone who will promise them this ("kid next door" syndrome).

The same way they can convince themselves that they've totally discovered the NEXT BIG THING(tm)... probably years of alcohol and drug abuse

In a word, "ignorance"

All the while we have rogue devs out there that go "sure, I can do that for 500 bucks on wordpress", then we'll have clients that believe them.

cheap ones like to find cheaper ones

There is no WordPress, only "Fucking WordPress"