You’re right, if the buyer’s agent isn’t getting that three percent from the seller, they gotta get it somewhere, but the real estate industry isn’t in a vacuum and they’ll look for it in some other industry.
So if a buyer’s agent will now charge money for showings, admin work, etc., there will be competition between agents to provide the highest quality services at the lowest/most competitive price. Which means that those agents who aren’t motivated to scale up and increase their quality will effectively get pushed out of the industry by agents who are.
Unmotivated agents who are just looking for a quick buck and aren’t getting their expected return with the minimal time and effort they put in will leave the real estate industry and look for that money elsewhere.