Most people want a smartphone. They don’t want a basic phone without web browser and on which you can’t install your favourite apps. That “basic phone” would be a small niche.
I think basic phones (with only phone and SMS features) don’t become obsolete unless GSM is shut down. App incompatibilities, slow-down due to current software and security holes aren’t a matter for these phones.
And if the hardware breaks down, give it to recycling and buy an used basic phone from ebay. Used phones from ebay save resources and are therefore very sustainable and eco-friendly.