why did the constitutional convention choose to keep slavery legal?

Many people, both north and south owned slaves as did many of the founding fathers (Jefferson, Washington, Franklin etc)

Slavery was already a bit of an issue and they did not want the whole thing to dissolve with states pulling out of the union, before the concept of the United States and the birth of the new country even got off the ground

I don't think they were sure they could be prosperous as a nation without slave labor as it has not been done before and to change something that radical might have spelled doom for a country that was brand new and often on the verge or brink of collapse for various reasons.

However, clearly, the fact that they choose to keep it, forced a civil war less than 100 years later and the quote you often hear is "Men who were alive to see the birth of the country may now be a witness to its death". A little overly dramatic and not true of course but that was how many felt. It is too bad they kept slavery in. We are still living with that legacy and it is a bitter and shameful legacy

@Manuela this question was about slavery not Jews and 9/11 which is not true by the way.

Many of the Founding Fathers (including Jefferson and Washington) were rich plantation owners who needed - and owned - slaves to keep their wealth rolling in.

They weren't about to create a government that was going to take that away from them.

Many Southern States would not have signed

They didn't think that the slaves would benefit from being free

they were racist