FWIW, I spent time at a large national "disruptor" broker and this is a non-trivial process. There are hundreds of MLS systems in the US, each with its own data, quirks, and synchronization issues. One has to manage so many feeds, cleanup, normalization, etc. Throw in the many data sharing agreements between various MLS systems and the simple act of deduping suddenly gets complicated.

For consumers, the value is that they can see an aggregate list in one place without having to sign up for them via an individual broker's site.

If MLS threatens to shut them off, that might be grounds for an antitrust lawsuit.

Maybe they're too afraid to risk the business on it? Maybe they did the risk analysis and decided it's not worth it?