> Why do we have that complex systems where shares can only be traded by regulated entities (brokers)

Because it safeguards against fraud and tax evasion.

> Paying 2-5$ fees on trades seem backwards this day and age.

Many brokerages don’t charge for buying or selling stock. They make their money elsewhere, likely with contracts on calls/puts. But to your point, having to pay a variable rate fee for moving my Ethereum from one wallet I own to another wallet I own also seems silly. I’m certain though that in both cases the charges cover the maintenance costs to keep the platform going. Everything comes at a cost.