From the code comments: "// The contents of an edit notice is unlikely to change in the 24 hour expiry window, so just record that a notice with this key has been shown." I think this was written by @Esanders?

I wasn't aware of the exact rationale before. If a new sanction is instated, having to wait 24 hours before knowing that everyone will be able to see it is probably not acceptable for communities. Admittedly, showing the notice more than once every 24 hours is probably not acceptable either. The 24 hours are, in my view, the least offending compromise. It's too short to avoid bugging regular editors yet too long to inform community members of new sanctions in a timely manner. Granted, it's better than no edit notices at all, but that's a rather low bar.

As far as bugging regular users goes, it'll take a while for complaints to start rolling in:

• At a rate of 1/day/article it'll take probably two weeks, maybe more, even for die-hard Wikimedians to start getting annoyed. People who only edit occasionally will probably never get annoyed.
• Not everyone will actually make a complaint. Many wouldn't know where or how to complain, others would believe complaining to be futile and the more tech-savvy users will find ways to suppress the notices. I've gone to great lengths to try and absolutely minimize the latter with ENOM.
• English Wikipedia uses EditNoticesOnMobile, so you won't be getting any complaints from the largest community.
• I suspect users from non-English projects might be less likely to complain, especially if their English isn't great. Or they would only complain on their local village pump in a language we can't read.

Just in case anyone wasn't aware yet: ENOM is public domain (WTFPL), so feel free to copy-paste whatever you can use.