Although I don't ride offroad I did notice that myself, I think (and I could be wrong) that it's because BMW are using TomTom's mapping service/system.
Whats even more frustrating is that if I search for my local J&S Accessories in Oakmere on
https://mydrive.tomtom.com it finds it, but if I do the same in the Connected App it doesn't. Comparing the map view it's clear that the BMW app is using TomTom's maps, but I assume an out of date version.
What I've noticed will happen is if you were to ride that route posted above, I'm pretty sure the instruction through the helmet comms would be something along the lines of "You are approaching your waypoint, it is on the left in 400metres" and it'll assume you want to just ride on past it without stopping.
I just had a look and the TomTom Rider 550 doesn't seem to have offroad routing options (that I was able to see) so this would seem to fit with what you're seeing. Which is a shame as I imagine alot of people who take their GS's offroad rely on following a GPS route.
The biggest annoyance for me is, theres been numerous cases where although I've not wanted to go offroad, I've wanted to navigate to an address which the Connected App/TomTom maps have no knowledge of so it's just kinda stopped leaving me to figure the rest out for myself, although I'm getting a little off topic now, apologies.