Having spent a decade in politically led organisations I wouldn't personally rely on them for long term planing. I still remember when our analysis team went before the elected officials and told them that if our citizenship increased from 50.000 to 60.000 then they would likely need bigger schools in 5-10 years because 90% of the people moving to our city were young families. Increasing our citizenship to 70.000 was part of the priorities from basically every political party, they even paid the top management bonuses if this was achieved. But the schools were never expanded. Then 5-10 years later when there weren't enough room in the schools and the parents started operating their own "free schools" (basically the same as public schools but more expensive for the city), the politicians spent 6 months trying to find someone within the administration to blame for not warning them that this would happen.

So the easy answer is that they bought them because they thought they were cheap.

Pixel 6 and later get 3 years of OS feature updates, and a further 2 years of security updates (5 years in total).

For comparison, all but the first 2 iPhones have received 4-5 years of support with the iPhone 6S being the oldest iPhone still receiving support almost 8 years later.

Android has been a complete joke when it comes to software support for older hardware, it's almost sad that it took proposed legislative pressure to change this.