Eh? I haven't seen a single router that monitors packets on the channel other than their own, not to mention management frames of other AP's

A deauth packet needs the MAC address of the AP to deauth clients connected to it and the MAC address of client you want to deauth, the latter is not required and an omission would result in the packet being treated as a "broadcast deauth" but many clients do not accept broadcast deauth requests.

"Auto Channel Selection" is done very poorly on most routers, there isn't an algorithm to do so in the spec and the vast majority of routers either to a round robin on boot up or default to channel 6 when set to auto, I can count on one hand the number of routers I've seen that run any type of spectrum analysis on the available bands before selecting a channel.

The only thing I've seen that even resembles closely to what you claim is that some ISP provided routers default to "disconnect" every 12-24 hours. Some just reset the DSL connection, but some also reset the clients. This is done primarily by cheap ISP's that want to free up IP addresses they basically reset the DSL connection and complete the handshake but does receive a lease until a client on their network attempts to connect to the internet, think of it as a standby mode.
To ensure that random traffic on the network does not trigger a lease some deauth their wifi clients to reset all existing connections. However this is pretty rare as most DSL providers just reboot the router remotely....

However again random deauth MGMT frames on the same channel would not affect your own wifi network since the MAC addresses of those APs are not identical, conflicting MACs could cause issues but they could cause so many other issues as well way before anything like this could become an issue.

I really don't know why home internet connection and particularly WIFI has so many insane myths and conspiracy theories around it.
The reality is simple the 2.4ghz spectrum is the most contested unlicensed spectrum in common use with everything down from your microwave to house and car alarms, wireless headsets and other wireless radio equipment using because that spectrum has been pretty much defined as unlicensed globally way before WIFI every became a thing.

As a result WIFI equipment and especially old and or cheap equipment works really poorly, and the fact that everything from your mobile phone to your toothbrush today comes with wifi and in many cases spams the spectrum even when it's not enabled only complicates the issue.

Then you have housing that outside of the US is primarily built out of reinforced concrete or bricks even for internal walls and you get the worst possible environment for a stable connection.

It's slightly better now in Europe as wood, foam and composites are becoming more and more common for housing both internally and externally but still I've seen flats in London that the wifi won't work from one room to another if the door was closed, we later figured out that the door had an old layer of lead paint and the flat was in a converted victorian town house from the late 1800's which was built from brick and still had lead piping, some of the windows can also be made out of lead glass especially if they are old and pebbled or painted if they weren't replaced recently (which if you live in a graded building they likely weren't because it would cost a small fortune), and some of the clay bricks and fire bricks may contain high levels of tin and lead naturally.