Just being in the mainstream kernel, instead of an out-of-tree module, already gives a couple of benefits. The code will always be kept up-to-date with the inte

Just being in the mainstream kernel, instead of an out-of-tree module, already gives a couple of benefits. The code will always be kept up-to-date with the internal kernel API, so you won't have a situation where the kernel is updated but the out-of-tree module fails to compile due to an API change. And if you're running a signed kernel (for SecureBoot), you don't need to have a complex setup to add an extra key and sign the module whenever it's rebuilt. Also, as others have mentioned, being in-tree means it's better integrated with the rest of the kernel; this includes making changes to core kernel code when they could help the module.