While Masters handled its waning years better than most shows do, I do think that it has been showing its age for a while. Season 3 had to bring in the fictional children to fill time in a lot of the episodes, while season 4 had to bring in two extra doctors to create office drama, so it was clear to me that they were running out of core material and having to make things up to keep the show going. I think it was time to end the show, but I am sad that it didn't really get a proper ending.
I'm rather shocked that only seasons 1 and 2 seem to be readily available on Blu-ray. Season 3 ended quite some time ago, but it's hard to find, even on DVD. I guess the odds of a complete series BD boxset with additional special features are pretty low.