Why can't I zoom in farther on a track (map disappears)?

[Frankie]

I've been using OruxMaps for several years. I like it, I have a subscription and donate, and have tried to understand its many features. One thing I've never understood: When viewing a track or KML overlay (with a locally-stored map), as I try to zoom in on that track  I am limited how far I can zoom in. I am trying to separate 2 tracks a few feet or yards apart, but can't do that without zooming in further. Even using Digital Zoom, it will stop zooming at some point. Some maps will zoom in farther than others, but all seem to have a limit.
Why can't we merely keep zooming even if the final map pixelates and becomes unreadable, in order to see details of a track or overlay in relationship to our position nearby? I'll try to attach examples. It seems to work better with PDF maps but I don't understand the reason why. Thank you for any suggestions.