They say:

"This is the next step in the standardization process, and it comes with stronger guarantees of stability and intellectual property protection."

I understand stability, and in the general sense I see that people feel they need to protect their IP, but in this specific case what is meant by "intellectual property protection"?

W3C generally requires Working Group participants to provide IPR licensing commitments for the spec in question [0]. As far as I understand, higher level of specification maturity implies stronger level of obligations, though the specifics of what specifically changes when were never clear to me.

[0] https://www.w3.org/policies/patent-policy/#sec-Requirements

I think it means protection from intellectual property claims in the future.