Some features that were previously implemented in loader (3ds injector), or in "main" Luma, although with limitations (language emulation via loader had known incompatibilities with few games, ARM11 exceptions had very limited space they could use because they used padding in Kernel11) were reimplemented in a better way within Rosalina (language emulation specifically uses a completely different approach, instead of patching the game for the desired region, interprocess communication hooking in Rosalina makes it possible to spoof the response to the game when it asks for the console region). The GPU protection svc which was stubbed by patching the kernel is now "stubbed" via Rosalina as it hooks the svc table, same for adding "CFWInfo" (the svc used by Luma Updater and stuff) and svcBackdoor. Disabling Rosalina in 8.0+ means fully disabling language emulation and then you get people complaining it doesn't work and all those important features (NTR and other homebrew wouldn't work without svcBackoor FWIW), or making a mess to maintain both approaches to *everything* in the code.
It's not as easy as you think.