hm… I suggest one major reason is money/marketing. Just at this current topic:
there are a lot of customers who are very disappointed.
Just let me provide one thought on that topic:
From a marketing-related point of view it is just reasonable to do a lot of DVR/live TV stuff rather then investing a lot of time in developing own-content-based streaming features.
Why?: The simplest answer is “money” 
I suppose that doing more TV-related stuff comes along with a large number of potential contracts with television studios etc. Also there is a great potential for placing ads etc.
There are currently enough platforms like Plex on the marked that only support own-content-streaming. Furthermore, we do not need another streaming service (like Netflix, Amazon Prime, Apple, Disney, etc.)… with such services you cannot watch and record TV etc.
I suppose that the Plex management sees the current development as a reasonable “next step” into a new decade.
Personally, I don’t see that because nowadays most people (I know) do not watch/record live TV. Okay… some sport events may be interesting… however, there are already streaming services that come along with extra packages for sport events (in Germany e.g. soccer).
Importantly (I can only speak of the German television), most of the TV broadcasting companies lost their rights to deliver famous sport events through their channels. Instead, you will have to buy sport packages from streaming services.
Plex cannot earn money by only supporting own-content-streaming services. There are already a lot of such services out there, and most of them are free.
Of course, we - loyal Plex users - think that it would be a unique selling proposition to have some very nice features like HDR tonemapping, dual-layer Dolby Vision support, GPU fallback feature, etc…
But keep in mind, the Plex management would always argue that this is - justifiably - uneconomic. They want to catch a bigger audience, and thus it seems that they abandoned their origins and focused on more “modern” features (like DVR stuff).
I certainly do not see that DVR will be the future, however, they do not ask me about my opinion 
There are a lot of more options to get a larger audience:
E.g. asking the current costumers about their needs and derive interesting (new) features…
… however, for this we need a friendly ear for such requests… At this moment, I do not see that.
My prediction for the future (3-5 years) is that Plex will completely stop developing own-content related streaming features and leave the respective users behind with unfixed bugs.
Of course, it will be possible but future new features will be not considered anylonger. In the worst case, Dolby Vision support was the last “big” feature that was developed.
I do not think that we will ever get tone mapping etc. Sorry, but I find it reasonable (from an economical point of view), even if I regret this. Such features are time consuming to develop and maybe also expensive (lincencing etc)
