You just have to accept that MUPS are multi use pathways and not fast biking lanes and adjust your riding style. Just as cars need to adjust when sharing the road with a bike. Suddenly the cyclist is the one in the heavier, faster moving vehicle.
I had this funny experience a few months ago when I started gravel riding a particular section of dike system near my home. On one section near the parking lot I could not figure out why walkers were being so disrespectful with their dogs, often letting them run free and not controlling them as I rode by etc... man, what's wrong with those people! Turned out that particular section (about 2.5 km) was part of an off leash dog walking park. Duh. Now I just accept that when riding through there I have to take it slow until I get past and onto the longer stretch of empty dike.