A lot of it is down to timing as well, e.g. when you bought into your last platform, and how rapidly new GPU's have become available, and how much the graphical API's change in that time frame.
Lets take an example of the 6700K, if you bought it at release October 2015, and at the time had a GTX 980Ti, you would have had no problems. Roll on to June 2017, and you've decided you want more performance in the wide range of games you play now, and have moved to a new monitor with higher refresh available to you, so you get a GTX 1080Ti, which is around 20-21 months after you first bought the platform, but the 6700K is still pushing the card to it's max in the majority of games.
Lets move on to October 2018 (the future) so far you've had the fastest platform available (for the majority of titles) and it's been your for 3 years. Nvidia/AMD finally decide to release faster GPU's to the consumer market, but only 20% faster than the 1080Ti, so you decide it's not worth it, and wait for the 1180Ti in August 2019, you've now had your whole platform for almost 4 years, and for 3/4 of that time you've experienced the best any system has to offer in the majority of titles. However there's a spanner in the works, the 1180Ti is being bottle-necked in some newer games by your lowly 4c/8t CPU (which you've had for 4 years), but still offers the ability to go toe-to-toe with the newer CPU's with more cores, and threads when the pure GHz makes the difference. It's reached 5 years now, and it's time to move on, since you can no longer put up with the stuttering and poor performance from your 5 year old CPU, but it's had a good life, and you've had the best years out of it.
What does it all boil down to? You've had the best possible performance you could get for more than 3/5 the life of your system, and for the last 1/5 it was almost holding you back, but you got the most value from it, for the longest amount of time. You can reverse the above, and swap out the 6700K, for the R5 1600. So you'd end up with worse performance for the first 2-3 years of the system, and possibly have the same or better performance for the last 2 years, that's assuming all you do is play games and not much else.
If for some reason you don't care about platform longevity, then all of this thread is pointless. I would say that 2017-2022 is going to be a huge shake up for the CPU world, a bit like when the Althon 64 launched in 2003, and Intel did an about face, and we saw the Core 2 Duo hitting shelves in 2006, that was a great time to be an enthusiast, we even had two players in the GPU market as well.