Getting back to the OP, RPGs are a little different, for reasons touched on in a few of these threads. Ho so?
Relative newness: 30 years may not seem new, but things like sports, fishing--as noted--board games...have been around for a lot longer. Definately a process of figuring out both what can be done in an RPG and working out many kinks...these are both issues in part due to...
Complexity: Even when they were short, the rules for D&D were longer then just about any convoluted simulationist war game. The range of activities that can be in game and can be in rules and can interact with other things is just more and more involved. Especially in a broad appeal game like D&D, which is meant to allow a lot of different people to play a lot...
Replay and scope: You can play that D&D charecter for many, many hours. That campaign can go for years, that world for decades. Issues that may not exist at certain levels, in certain situations, in certain character combinations, can arise in others. And you may not find it out for a while.
The trick to this is, as wng&swrd said, is evolution. All of the above imply a fair amount of change until the game works out a lot of issues. Some of which are still being worked out. One implication of evolution is that you are tied to the past, legacy issues get carried around like vestigal organs. Another is mistakes. Like bad mutations, some changes might not work as hoped. Finally, there is the people who use the game, and specifically D&Ds ever aging fan base, who both desire a better game but also one that they are familiar with.
The “answer”? Lots of experimentation at the margin, but true edition reboots only when needed and with real value added that reflects both lessons learned and new stuff that actually works. I don’t think any edition has quite got there. Still too much group think, designer preference, and condescension towards the fans, and yes, the problem of “we need money so lets make core books cause they sell the best”. However I do think that the game has in general gotten better, inspite of all this. It has evolved.