For me it's not so much trying to insult them for having a small dick, but insulting them for caring so much about having a small dick they feel the need to compensate.

Doesn't matter that their dick is small, just that they're so insecure about it they need to try and tell the world it's not true.

Two male apes park next to each other:

"You don't fit into the sociocultural group I'm a part of, AKA THE BEST GROUP, because you are not sending the right social signals! Therefore YOU ARE NOT A VERILE MATE FOR THE HOMINID FEMALES!"

"NO! CLEARLY IT IS YOU WHO WILL NOT SEED THE NEXT GENERATION OF OFFSPRING! Based on all the information I've gotten about appropriate social signals for my gender, age, ethnicity, cult, location and socioeconomic status, I am displaying the appropriate signals! So I shall point at you and say WEIRD!"

It's not about actual small dicks, it's just a symbol for insecure men

Well, I kind of agree with you, but also what I intended to say is that I think most pick up drivers don't feel masculine enough, whether it's due to a small dick or something else making them feel like they aren't "real men", so they compensate their insecurity by driving unnecessarily large cars.

Yeah, I maybe should have left the dick part out. A man can have a small penis and still not be insecure, and a man with a huge one can still be insecure about their masculinity and try to fix that insecurity with a stupid truck.

We'll get over it when egos and genetalia lose any correlation.

Not that soon, I'm afraid.