I think a lot of it depends on what one is watching.
I can name many movies that are extremely intellectually stimulating.
Just like I can name many movies and TV shows that demand one turns the brain off to possibly enjoy.
Honestly I think part of the problem is a couple of things, for those of us that tend to not get much out of TV and movies.
Firstly, too many things that are... braindead. Reality shows, for instance. Or things that are, how do I say... "mass produced for max profit?" Marvel movies, for instance, with their ultra-predictable storylines and extreme focus on spectacle (while not even always actually staying true to the source material, no less). That doesnt mean there's nothing good, but...
It's kinda like how AAA VS indie gaming is to me: The AAAs side of things is often busted and predatory, with genuinely good stuff being the very rare exception to the rule, but you hear about the problematic stuff the most because they come screaming at you and get in your face. The indie side isnt infected by corporate, but that also means they are harder to get at. For someone who is definitely tired of the AAA side, but doesnt know where to go for the indie stuff (or doesnt even know that stuff exists!), well... honestly that's kinda how TV and movies are for me. The derpy stuff is in my face. I have no idea if anything good is behind them because I cant see past those. I wouldnt even know what to look for anymore.
Also the extreme amount of ads and such REALLY doesnt help, nor does the chopping up of... everything. Correct me if I'm wrong, but it used to be that you just paid for cable and you got, well, cable. Lots of channels, one payment monthly. Now every stupid corporation wants you to pay them, and you only get their stuff for that payment, so if you want other stuff, well, better go sign up for 5 more things. Heck, I recently wanted to watch Columbo, right, as Youtube randomly threw clips of it at me and it looked interesting. First time I'd taken an interest in any sort of show in years. But that meant signing up for some bloody stupid subscription JUST for that. The mostly unused subscription to Hulu didnt have that (just as it doesnt have LOTS of things, since it's all so divided). I ended up just roaming the internet until I found a free (albeit wobbly) download of one episode, and that was nice, but the process of doing that more is beyond my patience, so that's the only episode I've seen.
Though it's the ads that bug me the most, personally. My family all watch a lot of TV (both shows and movies), and something I often ask them is "how in the world can you watch this? It's more ad than it is show". Often they arent even truly paying attention to what they're watching, it's so full of ads that their phones become more interesting. At least on Youtube I can block all that nonsense... I've got like 4 separate layers of adblockers running, nothing gets through... but I cant stop things that arent on my PC here, so I never venture outside of it.
That's just how I see it, anyway, others may have different views on it. Overall it's why I switched over to mostly watching Youtube... I used to watch TV and movies, once upon a time, but that was a long time ago. And even then, a lot of what I did watch was well before my time.