Getting a major OS update is almost like buying a new phone you get a host of new features, (hopefully) faster software and occasionally a complete overhaul of the UI. Its actually better than a new phone, its free!
Yep, phones never had the PC model where a new version of the OS is something you buy. Thats good on the surface, but theres a flip side. You can update a 10-year old PC to Windows 10 without waiting on its manufacturer. You probably shouldnt, but you can.
With phones, you pay nothing for updates and sometimes you get your moneys worth. Thats not true for all brands, of course. Google, for example, commits to deliver major Android updates to the Pixel 2 phones for 3 years (longer for just security updates). Sony just announced it would support its flagships for two years.
Thats fine, but the cost of the update is built into the cost of the phone we shouldnt have to tell you how expensive the Pixels are and Sonys more affordable phones dont get the firm 2 year commitment.
The upgrade potential of a phone is something we always consider it expands the useful life of a phone. We might not recommend a phone by a brand with a spotty upgrade history, for example.
So, how long do you expect makers to support their phones (all phones, not just flagships)? Obviously forever is impractical, but 1 year may be too little.