[error503]

There've been so many issues it's definitely getting confusing, but the thing blocking the MAX10 certification is a problem with the engine anti-ice system.

You're correct that this problem exists on all MAX variants, but those other variants are already certified (the issue was discovered post certification), and it's deemed to be not severe enough / with a good enough mitigation that they are allowing Boeing some time to come up with a fix for the already-certified design, and continue producing it. The expectation is that once Boeing has a proper fix and retrofit plan, it will be required by an AD on all aircraft. However it's unlikely the FAA will certify the new MAX10 variant with this known issue, and so far Boeing doesn't have a fix.