Uh, how about they want to make money? And they have to consistently pay their developers and other bills? Is this a serious question?
We all have bills to pay. Upping prices because I want more money isn’t a very understandable reason.
It’s not like we have any visibility into Plex’s costs. So it’s just as likely that the owner wants more profit than they have costs.
Things that were added in the last 10 years off the top of my head:
* 10 years of updates to the iOS/Android/GoogleTV/AppleTV/Mac/Windows/etc clients (that doesn't come for free)
* OpenSubtitle search built in
* Intro detection
* Credit detection
* Watch Together
* LiveTV/DVR support
* PlexAmp
* PlexDash
And more that I'm not thinking of.
You can say "I don't care about those features", which is a tired take IMHO, but there are plenty of features they have added to keep up with the online streaming platforms.