Ah...That's actually a good question. 9.6.1 has in fact proven pretty high quality. Nonetheless we do have customers (carriers usually, but also some of our hospitality partners) that do their own very extensive test suites qualified against a particular feature set (9.5 and 9.6 having different features). So it can be expensive for them to re-tool against a new major release vs an MR. There can be other dependencies - e.g. FlexMaster team might not be ready to upgrade at the same time.
We also have some RIOT partners that have certified their product against 9.5 but not (yet) against 9.6.
If you aren't under those restrictions and practice good upgrade hygiene there's no reason not to go to 9.6 if desired.
Since we maintain 2 "trains" at a time, when 9.7 ships (soon!) we will stop active development on 9.5, so this is expected to be the last MR for 9.5.
Hope this helps.
