It's very difficult to upload any image to Wikipedia, you have to jump through all sorts of copyright hoops. One of the greatest barriers to writing Wikipedia articles is that you can't get the source material, it's either not on the internet due to copyright, or it's behind a pay barrier, especially with scientific texts. It's hard. And the cost in time and energy of going to a library, then trying to translate from those paper sources to online is pretty high (impossible for many especially outside the US). It's volunteer work after all, how much time and energy do you have?