@2b2bff My guess, there are two reasons.
Garmin devices have weak hardware. In particular, all current Garmin devices have only 5 MB of RAM - fast access operating memory where temporary data, such as rendered map data, can be stored. My guess is that because of that Garmin can’t cache a larger rendered part of map that works be needed for the rotation. In contrast, Suunto watches have additional 32 MB of RAM for the map data.
Garmin maps are far more detailed, which makes rendering more expensive in terms of battery power use, and that is probably why Garmin doesn’t pre-render maps in background.
So when you try to rotate a Garmin map it likely has to pull the data from the storage and then render it, which is slow. The storage access is the likely culprit.
