In addition to this, front baffle width correlates with efficiency, i.e. modern narrow front baffle speakers need a more powerful amp, combine that with the necessary smaller bass drivers and you see why most modern speakers have crap bass
1. In the modern family, everyone wants to listen to something different. In the family of the 1960's to this was not possible, because too many kids, not room for so many big speakers, etc, etc.
2. Now, the speakers are there to carry the audio, status is derived from the size of the video screen. The screens crowded out the speakers. And you need 5 or more speakers now, which makes a set of big speakers exceptionally unfashionable.
3. Speaker size is inversely related to potential big box store volume because of the huge warehouses and sequesterd listening rooms that large speaker retailing would require. Buying without listening first makes does not fit with the idea of spending big on something that you need because your are elite afficianado.
4. The middle class is dead. In the 1960's, 1970's, or early 1980's, a 'good' stereo would cost about a month's net income for a median income worker. Today the good stereo still costs about a month's net income for a median income wroker, but the median median income worker is two weeks net pay away from homelessness or moving back in with his parents. And in that supposed golden age of stereo, the 'good' stereo was expected to last about 10 years and many of them did. Some are still working, many have been in the repair shop several times and keep going. Today, no one expects anything to outlast its warranty by much (except maybe a car), and competent repairs for anything more complicated than shoes are a not easy to come by.
That's a very pessimistic take. I recently sold a Sonos connect - about 15 years old if not older and working as well as when it was new. I have a Google home max speaker, 8 years old, works flawlessly. We have a pair of B&W speakers from 2001 or so - got the speaker insulation replaced, otherwise everything great. And a 5.1 set from Logitech from 2005 also works without issues - the difficult part is to only make sure the PC has the right outputs, but even that is moot with USB sound cards.
We also have some cheap monitor speakers, they work fine after 7 years.
