why do Sonos products never work ?

Yes, but if you have enough Sonos units with line in jacks, the Echo units can be grouped, and when wired to the Sonos line in jacks can drive Sonos units as dumb hardware even if the Sonos WiFi is turned off. Network reliability then is only to the extent needed for the Echo units to work properly there.

Once one uses the Echo units as front ends, one starts preferring their UI to that of Sonos.

Sonos is no longer the only road to multi room wireless audio in the home. Echo is one way, definitely offering more value via lower price points. There are probably many others as well, for all I know.

I moved to Sonos in 2011 and had no regrets leaving behind wired legacy kit; I moved from Sonos to Echo in 2020, and again, no regrets at all. And because I have enough Sonos line in jacks, it was a painless move that involved nothing more than getting in the right Echo devices ranging from a Show 8, to a Echo Flex that has less hardware than even a Dot, where a screen was not needed.

PS: I use none of the other “smart” stuff that Alexa offers, it is all turned off because much of that is still silly. All I use the devices for is as music sources, with optional voice control.

In my own system some SONOS units are on a 3rd party wireless mesh, some connect directly to my ISP’s WiFI, and others are SonosNet. There is an S1 and S2 system. Controllers can be wired, or connected to either WiFi. The system works well until there is an occasional blast of interference from a neighbor. There is a healthcare facility next door and a network scan can sometimes observe 70 nearby access points — some using very unfortunate channel assignments and widths.

SONOS requires more robust network support than simple web browsing, file fetch, or email.

If you dig around the Internet there are lots of ‘fires’ burning around ISP’s Gateways, my own included. From time to time, it will get its knickers in a knot and needs to be rebooted.

There is a large number SONOS systems in the field and the number is increasing. If all of these systems worked as well as the system described here, the number of systems in the field, would be shrinking, not expanding. 

Not every Sonos product I have @Kumar has a line-in - I have Play:1’s  Ones/SL’s, Move (v1), Roam x2, Ray, Beam etc. so I can’t add an echo device to any/every one of these products individually - so your setup may be okay for you and your hardware, but it’s not going to work in my own case and I suspect that will be the same for a good many other Sonos users too… The network reliability will still be a centre-issue for the majority of Sonos users, IMHO.

Since you’re now basically only using the old Sonos boxes as unconnected dumb amplifiers I have to ask: why are you still taking the time to post here? 

A fanboy question from an unexpected source.

No, a legitimate question by someone who is sick and tired of listening to your constant bashing, not to mention the claims of superiority of your “Echos into Line-Ins” hack over something which you have NEVER EXPERIENCED!

Patently false.  Here are some of things that Sonos speakers can do that echo speakers, or an echo/amp line in hybrid cannot do.

• Play from local libraries, as you mentioned
• Play from aux/line in sources.
• Play from TV sources
• play from bluetooth sources
• airplay
• Play from steaming music services that Amazon doesn’t support
• Add and remove rooms from groups on the fly.  
• portable speakers
• atmos music (Amazon may have some way of playing atmos music, but not anywhere near the quality sonos plays it)

Probably a few other things I’m not thinking of.  I get that many users don’t care about these features, and an echo based system is fine for them,  but to pretend they don’t exist is just silly.

Also, Amazon recently had an event to launch new products, one of them being a soundbar.  It doesn’t work with  Amazon echos, stream audio on it’s own, or anything like that.  It’s essentially a dumb speaker. Maybe Amazon is just capturing a market, but it doesn’t make me think that Amazon is really that invested in the multiroom audio market.

It amazes me how someone can speak so definitively on the capabilities of a system they have never once actually used.  I have coworkers who declare themselves SME’s when they are not all the time, but at least they have operated the system upon which they are claiming to have expertise..