I feel like it is pretty common for folks to come up with solutions to known problem in TTRPGs that have already been not just thought of but implemented, sometimes for years or decades. it seems more common in the years following a spike in D&D's popularity in particular, and these days the very online nature of D&D fans and "influencers" makes this reinventing of the wheel all the more visible.
Why do you think this happens? Why do people end up solving already solved problem in TTRPGs so much, as opposed to seeking out existing solutions? Is it simply the DIY nature of TTRPGs, or is there something more driving it? Is it happening more today, or is it more visible?
What do you think?
imho....
They are not re-inventing the same thing, they are refining on what came before.
D&D has done this to its self as much as anyone else, if not more.
From 1e to 2e to 3e to 4e to 5e = there are marked and Large changes to an otherwise same system (compared to how little GURPS or BRP has changed over the years for example). In fact, some updates (3 to 3.5) are really just a batch of tweaks and alterations that otherwise "fix" problems.
D&D isn't fun by the way its D20 rolls. They knew this, everyone knows this. So what do they do? = They add a second D20 (roll with advantage). Now its a Dice pool game (sure only a dice pool of 2 but still, its a dice pool mechanic 100%). And as we see with 5th edition, a majority of rolls players go for are With Advantage. This made the game rolls more fun as the odds to succeed were reasonable.
- it's a "Fix".
And its the
creators fixing their
own game.
So the same thing happens with other people. Black Hack, Mork Borg, etc - they are all trying to get a commonly known set of mechanics to do something better or more focused.
As well, not all "fixes" propagate into all versions of that mechanic core rules, and not all of them "fix" things. And in some cases, those fixes are not needed under other people's implementations.
D&D is not the only one. Exalted 3e was such a clunky mechanic system, before the edition was even completed, they released a new edition "Fixing" a ton of the rules (Essence). And sheesh, there are a dozen fan/influencer based hacks of Exalted to fix the mess its rules were. Funny enough, some of those fixes never made it into Essence, so then players need to re-apply some fixes to the game.... which can seem like someone re-solving the solved issue all over again.
...
TL/DR
Some systems never truly get the "solutions" to mechanic rules they need. And subsequent editions cause new/updated solutions to be applied/reapplied.