Got any concrete examples? I've been happily using LocalStack for roughly a decade now and haven't run into a single compatibility issue, aside from the obvious missing of net new services for the first N months after AWS product launches. Things like AppConfig, etc, but those gaps got filled in time. They clearly prioritized the 95pct/most used features of each service first though. There's a long tail in some AWS services, as one might expect. I've never used any of the more esoteric AWS feature sets of any of their services. Those are the things that tend to end up deprecated. So requiring those long tail featur sets may be the simple answer to having very different experiences.