Controlling the software is an integral part of the ethos of self hosting. Literally right in the first sentence of the wikipedia page.
https://en.wikipedia.org/wiki/Self-hosting_(network)
Self-hosting is the practice of running and maintaining a website or service, as well as own servers for e-mail, IM, NTP and so on, using a private server, instead of using a service outside of the administrator's own control. Self-hosting allows users to have more control over their data, privacy, and computing infrastructure, as well as potentially saving costs and improving skills.
instead of using a service outside of the administrator's own control
Plex is outside of the administrators control.