If two platforms share compatibility then developers can choose to target the weaker system and release on both.

For some games this might involve a bit of compromise and cause resentment with the owners of the more powerful system, but for other (simer) games it might involve any compromise at all.

Either way there are a lot of Switch consoles in the wild and there will be some publisher support for the Switch for a few years yet.

As an example from the other side of the fence ps4 is still getting titles:

opencritic.com/browse/ps4/last90