Same thing around where I am, often. In the larger parks with miles-long MUPs in them, it can be very problematic, with a great percentage of users being the motorized/electrified-type cyclists.

Severe speed bumps can solve the speeding problem, more or less. If enough of them, and tall enough to matter for anyone traveling greater than the safe-and-sane speed for such paths.

At least they can provide a dramatic result for those preferring to run 2x+ the speed of other briskly-moving occupants of those MUPs and bike lanes. Not that it would feel like a good thing for those having to navigate up and over all those, I suppose, and not that a town/city would like the added cost of such. But it would sure get the attention of the idiots who insist on dangerous speeds through sections. (A bit like the tough bollards, which many run into due to speed/maneuvering problems they bring to such paths.)