The founding fathers would be horrified that we let the slaves and women vote. We shouldn't put too much stock in what they think.

Wow, I take it you haven’t read much about them then? Because that statement is 100% false.

Then why didn't they write the founding documents so that black people would be free and women and black people could vote? Would have saved us a lot of conflict over the years.

Because, at the time, those beliefs were not universal, and a compromise was made as formation of the Republic would likely not have happened otherwise.

All the writings of the Founding Fathers are free and publicly available. You can learn all about it.

I like learning, link us to some quotes.

Like any subject, I’d you want a respectable understanding it’s going to take some commitment to studying key documents, not just reading. A few quotes.

You don’t get smarter reading a few 140 characters tweets.

That might explain the document, but that doesn’t explain some of them keeping slaves themselves. Jefferson even went on to be president and while he did things to restrict the trade, he kept slaves and opposed some measure to restrict slavery (for reasons much as you describe).

https://www.crf-usa.org/images/t2t/pdf/HowShouldWeJudgeOurNa...

https://en.m.wikipedia.org/wiki/Thomas_Jefferson_and_slavery

Because it would have tore up the social and economic fabric of significant parts of the US. The Founders were ahead of their time, but they still recognized that the vast majority of their countrymen were not.