You're overstating how easy these tasks are for many people. Doing brake pads/rotors or changing oil requires a driveway, some tools, and (for oil) a way to collect and dispose of the old fluids. Not everyone has access to those things - for instance, people who live in an apartment complex may not have the space to work on their car.
(Air filters are, admittedly, pretty easy.)
You can change your oil wherever you parked the car. A way to collect the used oil is as easy as an old jug of milk, or the empty bottles from your new oil. Disposal involves finding an autozone or someplace similar and dropping it off for free. In terms of tools you'd need, a $5 dish from autozone to collect the oil, a 10c copper washer for your drain plug, and a socket wrench.
Sure, everything you say was true for many folks 40 years ago too though! My point is, the processes haven't really changed for the common maintenance tasks over this period, people's perception of the difficulty certainly appears to have though.
Actually, in modern times you can buy an oil extraction pump off Amazon for $100, making oil changes so much easier than they were 40 years ago! A lot of [especially European] cars have the filter accessible from the top, meaning that you can change oil in 15 minutes in any apartment parking space by doing little more than popping the hood!
I’ve done oil changes decades ago but don’t bother anymore since I don’t feel like jacking the car up but using an oil extraction tool from the top does sound intriguing. Can you replace the filter from the top or does that require a jack? Also, does the filter need to be replaced each time?
Air filters are easy, but so what? They are even easier for the mechanic when my car is in the shop for semiannual maintenance.