Why is so much of the Internet still inaccessible to disabled people?

I don't know about "normal" blind people who are not software developers like me but I find most of the web accessible. I was able to successfully complete the R Programming course on Coursera with no sited help. I can do online banking, ordering off amazon, etc. One accessibility issue with Netflix was that they did not have audio description for video but this is getting better.

Because only a very small percentage of those that create the content are disabled themselves.