I am curious, why is that undesirable for you? I'm assuming there's something more than lack of individual app support for casting.
We have disney+, and my TV apparently thinks we're not subscribed. My phone does, though, and I can cast from that. Yes, we can watch Encanto again, but it's very jarring when the normal interactions with the TV don't work.
But when you cast from an application with integrated chromecast support (as e.g. Netflix) then the phone is free to use as you wish while the kids are watching. I do this all the time. I start the cast, then use my normal TV remote to pause, for volume control etc. You don't need the actual app for most things and you can use the phone/tablet for other things (I have to find translations for my wife, for example, while watching).
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One nice thing about the phone apps is that you can search for a different thing to watch _while_ currently watching something. Fast-forward/rewind also tends to be a little more intuitive with adraggable progress bar, except small-scale rewinds (1-2 minutes) of a movie is _harder_ because a few pixels is difficult to select cleanly.
I will say though that Prime is _freaking fantastic_ when streamed from my phone, better even than using the native TV interface. The Prime phone app lets you navigate _by scene_ in a show (e.g. Bosch) which my tv app won't let me do. I wish Netflix and D+ would/could copy that, specifically. I wish it didn't have spoilers in scene descriptions, but being able to say, "Hey go back to the start of the council of Elrond" is really nice, rather than having to use +/- 30 second increments.
Google in particular is the worst offender here because they actually had Miracast in Android all the way up to Nexus 4 - and then deliberately removed it! Other vendors of Android devices generally reinstate it in their distros, although I do wonder how long that is going to last (probably right until Google makes not supporting it a condition of getting Google Play certified).
Casting from a phone is a terrible experience. I want to sit down on the couch, mash some remote buttons and watch something. I don't want to find a phone to cast from. Whose phone would we use? Mine, my wifes, my relatives who are over? What if they want to change the program? Now they are figuring out all the casting business? No, pick up the remote and use it like normal.
Why is it undesirable having to go find my phone? Because I'm relaxing on the couch I guess?
