It’s a essentially a giant network effect.
Practically, the #1 reason to use a realtor is that if there is an issue with the home that should have been known ahead of time, there is a chain of insured entities that provides legal recourse.
The shop and decide part is secondary to their value, but that is how they are so entrenched. The local MLS in any given area has the ability to cut off access to anyone. Some are even privately owned. In order to disrupt an area, you have to get a slice of listing larger than what’s available in the local MLS and then get more people’s eyeballs on those listings than the combined circulation that the existing MLS feeds were getting...and then still have some means of showing the houses in person.
And you have to do that for EVERY single market you enter.
A young buyer is welcome to shop for a home without using a buying realtor...but there are still very high odds that the seller used a realtor on their end. The only difference in that situation is that the selling realtor doesn’t have to split the commission and pockets more of it.
This is ironic too, because realtors are more valuable to a buyer in most cases and there is more work involved for buyer representative realtors with no guarantee of a payoff.
The entrenchment remains because realtors will often avoid FSBO showings and sellers aren’t interested in experimenting...they just want their house to sell.