Limo is designed soley to work on linux.
NM is multi-platform, ie, linux is an afterthought, after Windows.
Also Limo currently 'actually' has more functionality with a much more broad variety of games on linux than NM does... in that it works for literally any game.
Both 'apps' have been in development for about the same amount of time, and Limo has delivered far more linux functionality, with far less jank and bugs, in the same timeframe, thus indicating Limo is much more serious about linux support than NM.
Just go look at the issues section of the github for each and you can see that for NM, there are tons of major problems with both the released AppImage and people trying to build from source on linux.
The Nexus folks either are not prioritizing linux, or are not very good at developing for linux, or both.