You made many valid points. As for reasons not to rush, there are a few that come to mind:
1) rushers tend to max the troops they use. In the future, sc may nerf a troop and buff another less used troop (e.g. hogs and valks, respectively) and you will be stuck with level 1 with said troop, where the maxer may be ready to go with a high end or maxed troop using a new hot strategy.
2) visuals/aethetics. Can't agrue that maxed bases look more bad a$$
3) high end clan recruitment. Many hardcore clans have requirements of "no rushed bases" and/or "combination of lvl 50+ heroes" for example. This a barrier to rushers that some maxers may not have to endure (taking into consideration some clans want maxed TH8s too, not just 9s and 10s)
4) what's the rush? This is one of the best games many people have played in a while. What's the point of getting from point A to point B the absolute fastest, only yo get sick of the game quicker than if you took your time maxing? Some people wanna ride this out as long as they can, with no new mind-blowingly great game on the horizon. Might as well enjoy both the offensive as well as defensive greatness of this game at all TH levels.
5) there's a sense of accomplishment given when you max out bases. It's not for everyone, but for those who enjoy it and for those who are OCD like that, it's a good enough reason to max.
Just throwing out some discussion points. I am fully convinced there's no one absolute right way to play this game, and I've heard fantastic reasons from both extremes that I can respect both types of players and any players in between. Just makes sense to play the way that gives you the most enjoyment.