I feel this video misses the mark pretty heavily on why this particular platformer failed and why indie platformers in general have failed/can fail. Two of the things it hit right were saturation and price. However the false resurrection of platformers began back when YouTube was more of a baby and game guide sites were emerging for flash games.

Flash games were relatively simplistic to create a platformer, and caused a lot of free decent platformers to emerge. Flash games worked on a different budget all together and were largely driven by ad revenue - one game would earn developers between $2000-$20000 depending heavily on how popular the game was, the initial sponsor, and how many rebrands flash consumption sites paid for. This was the underlying push for platformer flash revival, and super meat boy took a simple formula and made it simpler- a flash platformer with short difficult levels and used completion principles which were getting popular along with the rise of meta gaming. It was it easy to replay those levels over and over with a real end goal.

A number of these games were decent, but not all of them were popular enough to give rise to games outside of the flash scene, as the rise of mobile games quickly followed this making ad revenue more accessible from free phone apps(which quickly became saturated and was quickly realized to be a different beast all together all with media differences). One of the other notable platformers from this era was VVVVVV which gained success in a wildly different manner. This game probably only gained the hype it did due to the leak during its alpha phase that ended with it on 4chan, and then the developer ranting about how his game was going to fail because of pirates, which caused a lot of people to feel bad about the leak, since they thought it was a publicly available free flash game. This caused an influx of donations which set the dev on the path to success, since the game was pretty much complete at that point anyway.

Anyway after all the TL;DR the main reason this game failed was because it had little to grab the user beyond the one gravity mechanic seems like. That and a 10$ price tag is ridiculous when comparing it to the darker indie platformers. This may have been fine 10 years ago as a flash game, but probably would have raised the same amount of money in ad revenue as it got from sales.

He says the amount of games coming out hasn't really increased, and that more games used to be on other platforms instead of steam. This article says that were more than 5600 games on steam in july 2015. 1600 of them came out in 2015 alone and 1800 in 2014 compared to only 561 in 2013. It could be that a lot of games were only on other platforms before, but I doubt it was that many. Making a game has become much easier over the last few years thanks to engines becoming cheaper and easier to work with.

The over saturation and the impact of sales and bundles has made it harder for games to be successful. Why would I buy a game for $10 if I can get 3 similar games in a bundle for only $1?