They begin beeping at a random time between 8 and 24 hours after separation, not immediately. Probably it was still too soon?

It's a tricky timing to work out, I guess. You want to warn people about trackers near them, but you don't want someone e.g. leaving their tagged bag in their locker to cause loud beeping after 30 minutes.

I’m sure it’s trivial to physically disable the beep speaker.

Indeed, a Google search is enough to find guides, and I assume most bad actors would be aware of this.

Well, anything that involves precise drilling isn't really what I'd call "trivial". But it's definitely doable.