Hardware routers can be killed for many reasons. Age and an inability to upgrade them to suit current needs is the biggest one. OEM’s do this fairly quickly as they build devices with the resources to work for today and maybe tomorrow. After their product is no longer made they want it to be obsolete not long after so they can claim they can support is no longer viable. Then you but another router and they make money.

OpenWRT tries to augment and support devices for as long as possible but at the same time the hardware limitations still exist and often the storage will no longer support the latest version due to the size of the new version.

As far as when that will happen depends on multiple factors that have the ability to change at any time. There viable be a massive flaw in a portion of the software that requires a huge rewrite and the addition of code that will make the software too large to fit.

Sometimes someone will create a version with less used features available so that it can still be used but it’s a losing battle

If you want true longevity repurpose an old computer into a router. OpnSense is what I use and recommend. Add in something like a TP-Link EAP650 or two and you have a rock solid platform that can handle a lot more and last much longer. Add Power Over Ethernet (POE) along with an Omada controller and you can position the AP in a place where it will work the best for your use. You can have enough access points to have a full signal anywhere even if your place is the size of the Louvre. When new technology comes out you can upgrade the AP’s as needed when needed and upgrade the router as well in a similar fashion.