The Constitution doesn't say "all men are created equal"-- the Declaration of Independence did.

This was far from a settled issue. We take for granted that we think of all people as "people" with "inalienable" (can't be given or taken away) rights, but the idea had to develop and grow and be argued at some point before it joined the standard zeitgeist. Whether people held as slaves were "people" at all was, for lack of a better term, a hot-button issue of the day. To wit, here is a grievance against the King from Jefferson's original draft of the Declaration that was cut from the final version:

"he has waged cruel war against human nature itself, violating it's most sacred rights of life & liberty in the persons of a distant people who never offended him, captivating & carrying them to slavery in another hemisphere, or to incur miserable death in their transportations thither. this piratical warfare, the opprobrium of infidel powers, is the warfare of the Christian king of Great Britain. determined to keep open a market where MEN should be bought & sold, he has prostituted his negative for suppressing every legislative attempt to prohibit or to restrain determining to keep open a market where MEN should be bought & sold this excrable commerce and that this assemblage of horrors might want no fact of distiguished die, he is now exciting those very people to rise in arms against us, and to purchase that liberty of which he has deprived them, by murdering the people upon whom he also obtruded them; thus paying off former crimes which he urges them to commit against the lives of another."

Note he specifically refers to slaves as "MEN" in all caps.

Note also that Jefferson owned slaves himself and yet was outspoken about the evil of slavery. He saw slavery as an economic condition in which he was "trapped" as a beneficiary, and that it would take more than a declaration from an authority-less congress to end. If the Second Continental Congress had declared slavery immoral and unanimously supported its abolition, would it have turned the colonies against slavery? Probably not. It eventually took a civil war to end slavery, and its legacy lasts through today in one form or another. And anyway, Jefferson was certainly willing to continue owning people himself in order to maintain his social and economic status, despite his criticism. So clearly it was a complicated, contentious issue then.

I would be remiss not to point out that "men" is itself exclusive of, oh, 50% of people. And that the Constitution does not specifically define who can vote, but that at the time it was reserved to free white men with property (some states even had acre requirements on top of that). And as long as we're putting "person" in the context of voting, we exclude lots of people from voting: people under 18, non-citizens, felons, etc. Not all rights are created equal, even today.