You're absolutely right.

Higher rates align incentives because they make the provider more vulnerable to reputational effects. If you're targeting $150+/hr projects, you can't use online platforms to find clients. That end of the market simply depends almost exclusively on reputational marketing (referrals, industry contributions, mindshare).

Hence, as their continued ability to get contracts depends on having satisfied customers, higher-priced shops have an inherent incentive to deliver quality. As opposed to low-end shops who are just scooping up clients with their low rates and therefor have no quality incentive.