I imagine a travel agent would have local knowledge and connections, and would know the quality of the hotels they're trying to send to you, a high commission isn't worth it if your customer is unsatisfied and goes to a different agent for their next trip. Of course this is based on the assumption that the customer always wants to use a travel agent (an unrealistic assumption nowadays, because it's so easy to switch to the Internet).
Someone like Rick Steves(1) still goes to the destinations every summer to check out hotels, restaurants and local companies, I imagine someone with more budget would travel with his company rather than try their luck with some booking.com hotel with a high rating...
What you're imagining is what it was like in the 1980s, or possibly now for a boutique place, not the reality of the post-internet high-street travel agent.
You're not realising the reality of the typical high-street worker, and the sheer lack of autonomy that they have in their roles.
Someone like Rick Steves(1) still goes to the destinations every summer to check out hotels, restaurants and local companies, I imagine someone with more budget would travel with his company rather than try their luck with some booking.com hotel with a high rating...
1: https://www.youtube.com/@RickStevesEuropeOfficial