Android devices are generally newer and have much stronger hardware than WinCE based. On the other hand, WinCE is very minimalistic and maximally optimized
Primo is completely stable, works perfectly, but there is not (much) room for improvement
It does the job it is intended for completely (independent offline navigation)
NextGen is simply more modern, more configurable and of course with full support for online services

Apart from somewhat higher hardware requirements, the lack of additional skins (although it is possible to use some of those for android, I think Wandel skin has that possibility), the real problem is "only" that one - licenses
Software without licenses is absolutely useless

In fact, if someone managed to completely cr*ck the NG exe's the way it was done with Primo, then that wouldn't be a hindrance either
But it is much more complex to "break through" them, and apparently there hasn't been enough interest for years
The WinCE platform has been dead for a long time, but it continues to live through devices and beyond