I'd like to draw a line between certain processors. The cutting edge for any series will obviously have different requirements. WCing in general becomes tremendously important if you are building a compact system, or if you intend to overclock the snot of hardware. I've built my own WC loops, back before it was "cool". When you used RV water pumps, silicone glue, and car radiators. I fully understand anecdotal evidence is anecdotal, but as a long time observer, the number of people who "get their feet wet" is miniscule to the number that just build a system.
I will acquiesce, AIO's are more popular than ever, but I also want to point out, they are not really worth the extra cost, if a large heatpipe cooler will fit. Every system built by the end user will be totally unique. I'm not going to overclock my cpu. I gain nothing by doing so. I can also chime in and say, its been running 100% usage for several weeks and the tower is barely warm to the touch. The cpu is steady at 75C. I'm willing to bet, even in the category of people who build their own computers, watercooling makes up for <1% of the population, and if someone tole me 1% of THAT 1% built their own water cooling, I'd believe it. i'm willing to bet most people use the stock cooler, and even if they replace it, its likely to be an inexpensive air cooler like the hyper 212. (random example)
We need to be careful of being in an echo chamber here. Its very easy for a room of computer people, to agree with each other that "everyone" does a thing, when in fact, its just a percentage of a percentage. Watercooling and overclocking are fringe aka niche activities.
It is a mistake to think you can solve any major problems just with potatoes.