It's more that they are collectively overpaid. As house prices rise the %-based commission causes new agents to flood the market, lowering the number of houses sold per agent. Agents then spend a lot of time acquiring clients in competition with each other.
If you think about what an efficient use of realtor labor would look like it would be ~2 houses a month or more with agents spending all their time on showings and contracts. In a market with $1M houses this would yield roughly 24M * 0.025 = $600K/yr and up.
Hence the market becomes flooded with people that would like to make $600K/yr on a educational investment period of 6 months or less (plus an apprenticeship-like paying job for a few years).
The industry is weird because the price of agent service is resistant to supply&demand forces for various reasons but the main reason is that it's impossible to know what the selling agent's contribution to the house price is, since you can't sell the same house twice under the same conditions.
In principle, a good agent can easily recoup their commission by adding a few percent to the house price, but in practice agents have a counter-incentive to this because the homeowner will never know what the added amount was and raising the house price a small amount adds less to the agent's bottom line than moving on to the next house more quickly. In most cases the agent is simply setting the price that will sell the house quickly for the local market. As a seller, you'd probably prefer to make an extra 20K on that 1M house by showing for a month instead of a week, but this makes the agent do 4x the showings to make 2% more commission.
Ironically, the buyers' mortgage lender will have an impartial professional estimate done after they've already agreed on a price with you. In a perfect world, the seller would get this estimate done up front and then the seller's agent would be be paid on a structure that incentivizes beating that estimate. But wait - if the mortgaged portion of the price is greater than the estimate then the buyer's lender will back out ($collateral Quite the free market, eh?