Hello, Spine already checks for updates and automatically updates itself. If a new launcher is required, it is a rare event and Spine requires manual download because if it simply could update those components by itself, it would.
Spine will still update itself even if you don't update the launcher, but at those rare times when the launcher changes, speed improvements or other core features that don't usually get improved, receive an update, the most recent case being the new export features requiring new Java features.
If it can reassure you, this is also the second time I had to update the launcher in 4 years, the previous time was for using Spine v2.