Part of the problem is manufacturers.
Until the manufacturers are forced to write security patches & updates to their devices for $X# years after the devices end of life, they hope we'll just buy the newest shiny in order to get a newer, more secure, & supported version of the OS.
Fuck that. Stop buying the newest shiny, get one that does what you need at the best price you're comfortable paying, & only replace the device once it dies entirely.
Since we can't count on OS updates for more than perhaps a month or two past the device launch, & they want to charge exorbitant prices for dubious "improvements" (oh lookie! This one has a front camera with half a megapixel more than the last one!), then buying from some grey market generic not only makes sense (if the "big boys" won't update either then why bother using the OS version as a selling point?) it makes Cents (as in saving a metric fucktonne of them over buying the new overpriced shiny).
Dear manufacturers. Either start supporting your devices for far longer than you've been doing now, lower the prices to something not a sick joke, & stop "improving" the models with shite like removing the headphone jack, and maybe, *MAYBE* we'll start buying your stuff again. If you refuse to support them, refuse to price them reasonably, & insist on stripping much needed functionality out of the devices & calling it "progress", then we'll vote with our wallets.
You've just seen what such voting can do, so shape up & fly right or we'll *bury* your worthless arses.