Usually because the AI is working from inconsistent or outdated facts about you spread across the web — and it has no reliable, corroborated version to trust. If your hours say one thing on your site, another on an old directory, and a third on a stale profile, the engine picks one, and it's often the wrong one.
The fix isn't markup. It's consistency: make your name, address, phone, hours, services, and service area identical everywhere that matters — starting with your Google Business Profile and Maps, since that's where several engines get their grounding. Then get independent sources (reviews, listings, mentions) saying the same thing.
This is exactly the gap we're building tooling around — the difference between what's true about your business and what the internet can currently prove.