Even 5 year support for Pixel phones is new with the Pixel 6 line. Previously it had been 3 years max.
Qualcomm is such a ridiculously horrible company to deal with. They're in the business of selling new SoC designs every 6 months and trying to support a device for more than a few years is considered a massive opportunity cost for them.
It's the same concept as Apple mulching old MacBooks so they don't enter the used market except killing them by lack of software support instead.
They have an absolute stranglehold over the SoC market in the US. Samsung made a stupid deal back in the 90's to license CDMA patents in exchange for not selling SoCs (eventually Exynos) in the US or to any other manufacturer for that matter. At the time it probably made sense because Qualcomm agreed to use Samsung to manufacture their chips, but the deal is so hilarious lopsided these days. 30 years on and Qualcomm still won't renegotiate. It might've drawn regulatory ire if Samsung wasn't a foreign company.
Something tells me there's something wrong, either with Android or with Google itself.
People are used to desktops and laptops chugging along until they get tired of them being slow, rather than their device or OS vendor cutting them off.
https://support.google.com/chrome/a/answer/6220366?hl=en
If Google can do this for Chromebooks, most of which aren't even designed by Google (although usually based off reference designs), clearly they can also do this for the actual phones they make and sell under the Pixel brand. And Chromebooks span quite a wide variety of hardware capabilities, from school-targeted low cost models with eMMC and <4GB RAM all the way up to devices with NVMe and gobs of RAM on cutting edge CPUs from a variety of manufacturers, both ARM and x86.