Are you a minor? In my area minors can only work between the hours of like 6am and 7pm, meaning they can’t work open or closing shifts. If there are too many, it becomes hard to schedule people.... that could be why :/

On top of the minor laws, it’s possible that they need positions filled that are during weekdays and mornings, rather than the weekends and evenings hs students usually do. At my store we’re very few baristas who can do weekday mornings, all the rest are on school time so that may be why

I’ve never heard of there being a limit. What’s most likely is that the laws and regulations surrounding employing minors limits your availability and that store is looking for partners with more availability and flexibility in their schedules.