There's no real reason they couldn't but polling systems tend to be the first thing implemented as conceptually they are simpler and require less rigor to enfor

There's no real reason they couldn't but polling systems tend to be the first thing implemented as conceptually they are simpler and require less rigor to enforce. Switching from a polling pattern to an event pattern however is a sizeable amount of work required and you can frequently get bugs in the switch. The discussion here is in the context of a greenfield project where such concerns aren't an issue. To be clear it's not like an event registration system is better in every way than polling. It's trading some extra hd and (potentially) memory usage for upfront and cheaper cpu costs. It is possible that whoever made the decision weighed the two options and decided on polling instead of events, and this decision was made long ago when os filesystems were first being designed and storage was at much more of a premium.