Nobody is forced to do this. You're more than welcome to sell/give/etc your speakers to someone else.
There's a reason why the saying is "reduce, reuse, recycle" in that order.
They also don't verify that you recycled it, practically it only makes sure that the otherwise working speaker is removed from the market so that Sonos isn't competing with itself. I'd imagine that a lot of these just end up in the garbage.
If this truly was an environmental initiative, Sonos would rather take a proof of receipt of you giving your previous speaker to an e-waste recycler or even giving away to some place like Goodwill where it'll get reused.
They could just make sure that you were nice and gave away your device for free and/or charity purposes, instead of bricking it forever.
"Sonos's “recycle mode” intentionally bricks devices so they can't be reused" Fuck this kind of masquerading profit hunger as environmental responsibility.
Just buy some wired, maybe simple Bluetooth speakers for cheaper (eg. Sennheiser, Audio-Technika or JBL) and enjoy their fine sound.