I have another suggestion which doesn't contradict yours.
When I was younger I used to get bored way more often. I had to wait regularly during a week (e.g. for a bus, friend, appointment) or even at work as a software dev (e.g. compilation which used to take more time). This was also the case when doing some physical activities which didn't require lot of thoughts.
Back then, before mobile phones with internet access, you were either reading something or alone with your thoughts in those situations. This was when I had time to think back at things that happened, processing the information I had, refining ideas etc.
Nowdays those are often situations where we ingest more information like listening to podcast, reading stuff on the phone, etc... or situations that just doesn't exists anymore having optimised our work to remove those waiting points.
I personally find myself with clearer thoughts when I break those habits and give my brain some time to be bored again.
I do think there is "lack of boreness" epidemic leaving people with way more raw thoughts and way less time to process and challenge information, leading to some form of exhaustion and lack of clarity.
I doubt that's the only factor, but I agree that it's almost certainly a factor. The modern "tech" industry has filled our waking hours with unceasing demands to do something. Buy this product, watch this video, listen to this podcast, react to this social media post; even "practice self-care" has somehow turned into an obligatory virtue-cultivating task. We obviously had advertising before, but this is a different beast, something akin to living in a casino.
As Bo Burnham put it, "apathy's a tragedy and boredom is a crime".
I too subscribe to theory that "being bored" was an important part of our day to day lives. I think it gave us time to basically decompress and "defragment" our minds, and that is also when a lot of novel ideas or clarifications would come to us. Now having 24/7 entertainment at the tips of our fingers is almost completely removing this extra time from us, and there is much less processing that actually happens.
Definitely. Much of the structure of internet media encourages constant, passive consumption. Or, to use the terms of the grandparent, we move traded ambient thinking, reflection, and imagination, which the brain is pushed into during boredom, for ambient consumption.
I think a lot of people believe that, as long as they consume "high quality" or more intellectual content, the negative effects of constant consumption are mitigated, but I think that's false. It's less about the content and more about the structure and process. If you never give your brain moments to stop basic processing of wildly different inputs and to just critically examine them instead, you will suffer brain rot, even if the content you consume is "educational".
Sleep is also a forced meditation, so we can't avoid processing information. But in a different way of course.
Being bored, showering etc is well known to engage the DMN (Default Mode Network) where your brain connects pieces together from larger, more distant areas together. We as a society are missing this and its obvious.
That seems less likely then people being tired and stressed from the costs of living and the increased economic instability.
We have smartphones but we're perilously few missed pay cheques away from not having a house, with a capital class gleefully telling everyone how they'll all be unemployable very soon.
I have another suggestion which doesn't contradict yours:
This is only a small part of it (tech addiction 24/7 via phone); certainly there is something bigger at play, here (e.g: "the brain isn't the same anymore;" agreed).
I do not use email nor a cell phone (several years; outgoing landline, only), so I have more than enough time to ruminate (and read a few dozen books, annually) – and yet agree very much with OC's theory on needing mental health exercises to replace our newfound AGI tools/workers.
As an extremely conversive person (unbound by a cellphone), it's become an extremely strange world, particularly when talking with strangers, even in just the past two years. It's like: everybody is just mentally exhausted, mortal.
I know I am.
–Phoneless