Deserts are bad.
“Crossing the Sahara by land was impossible. The desert is massive. Miles and miles of nothing. The distance to cross it was just too great. The only way through it was through the Nile, but even then the Nile was not navigable as you entered the Sudan area.”
https://unchartedterritories.tomaspueyo.com/p/why-europeans-colonized-america-before