The matter is that the vast majority of the design of tabletop rpgs are spin offs of the original design of d&d...
The fact though that 95% of the rpgs follow this kind of system shows that most rpgs are not grown up by some genuinely innovative idea or intellect behind them. The chances that they manage to produce something explosive while trying to follow or mimic an established mindset are pretty slim. This is my impression at least.
If the RPG industry was based on creativity alone - if the market worked that way, then more gaming companies might create new games/new paradigms, but in the real world that is not the case.
One could argue that any RPG game, even if completely unlike D&D is a D&D spinoff. D&D was the first; the game that created the industry. D&D, no matter who owns it, as long as its a viable company will always be the example measured off of for RPGs.
Most indie developers have daytime jobs to live on, and work on their games as a labor of love and perhaps building that "most awesome new game". While some games can take off from such a start, in this business you need a market to survive.
I don't see these spin-off versions of D&D, as "not backed by true intellect and innovation" as you put, but pragmatists that need at least a trickle income to make any headway as a 3pp. That means accessing the same D&D market that is the largest chunk. By creating a completely different game you are lessening your odds of acquiring fans from the D&D casual gaming market. You have to look somewhat like D&D or you might never build a market.
These 10,000 (and growing) "spin-offs", many of them are innovative, yet still practical as a D&D group can easily switch to the new game, due to similarity in rulessets.
If a small RPG developer can gain some foothold, build their own solid market, based on D&D at start-up, now they might have the resources to introduce a completely different game that might mean something. If they tried this a start-up they would most likely not survive.
Your "impression", if thoughtless, seems lacking in business acumen.
Perhaps I'm reading you wrong.
GP