They last a decade. I could easily not upgrade my CPU for another 5 years and simply get less FPS, but still be able to play whatever comes out. It makes me want to cry. If you buy a 10 core broadwell, you won't have to upgrade until we got people living on Mars.
Isn't that good though? I remember the old days where I had to get a new CPU/platform every 2-2.5 years max. Now, I only have to worry about monitor+SSD/PCIe SSD+GPU. Less $ wasted on new mobo+CPU+memory is more $ I can use towards components that actually matter. Alternatively, it means more $ that can be used towards other hobbies, travel, gf/wife/kids, alcohol, sports, etc.
Would you really want to go to the old days where we had to drop $500-700 on a new CPU platform and 24 months later there is something 50-100% faster, but instead of 50-100% bonus performance, it was basically required to play next gen modern games.
Today, we have the option of buying faster CPUs to match with 120-165Hz 1440P monitors but at the same time, it's not a requirement for many AAA games when targeting 60Hz. I find it refreshing that now I can go out and buy a new Intel i7 and not worry about upgrading it for 5 years, unless I am doing it for fun/features.
I would accept requiring CPU upgrades every 2-2.5 years IF we got next gen physics and AI in games. If next gen games requires 8-16 core CPUs to increase realism this way, I'd be pumped and not care about the cost of upgrading since there would be a real, tangible benefit. But since that's not happening and physics/AI in games is a state of stagnation, it's very hard to justify wanting to drop $600-700+ on a new CPU platform for "fun".