https://itch.io/games/in-jam 352k
https://itch.io/games/exclude-jam 782k
I would not say that it is mostly devs doing jams here, what with twice the games not being in a jam.
With most games using some sort of engine, the accessibility features should be done at engine level. A single developer has neither the time nor the expertise to develop these things every time. Same as a dev would not implement a save mechanic for a renpy game. It comes with the engine. You do not want to have each developer coming up with their own clever way of saving.
Also, most devs will not have the capability to even test out their accessibility features. They cannot even test the game for different platforms. How does one test a color blind mode, if one is not colorblind?