The cotton-picking texts are another sick Democrat trick, and if you trace your call, you will see their source is not Trump

Railroads and the Cotton Gin Freed the Slaves,
yet not out of Republican Benevolence... maybe Free Soiler and Abolitionist Fervor influencing as a tiny zealous faction of the fairly recently formed Republican Party to replace the Whigs

,,,for the North wanted to win and not let the South use Slave Labor to Build their 2 Southern Routes.
& eventually the Emancipation Proclamation, yet that didn't happen until Jan. 1st, 1863... quite some after the April 1861 calling up of 75k troops to Ohio to be trained by a Democrat in McClellan, whom was the President of a Railroad and had a lot at Stake. (Stakeholder Capitalism 1861 style)

The Northerners, Repubs and Dems preferred to confiscate Land from the Southerners,
and use the cheap Labor that China, Ireland, & Germany were willing to supply build the first route completed, take over the Southern Route through Reconstruction and build it too with Irish labor...;
& then connect San Diego with Tacoma; and Tacoma eventually and lastly with Twin Cities Minnesota,
All Not Using SLAVE Labor, yet cheap cheap cheap labor of servitude, then citizenship for everyone except the Chinese.

Those Northerners: both Repubs and Dems were sooooooo nice to call up 75k troops to train, then send in against their own former states united, yet seceded.

Why is it that the former slaves weren't hired by the Northern Republicans as labor in any significant number, to earn money and build a free citizenship life in the West?

Yes, the CIVIL WAR WAS ALL ABOUT SLAVERY... It just took awhile to figure out what anybody was going to do about it whilst fighting over the ability to make a buck with Railroad Control, and control over Natural Resources, Iron, Steel, Rails, cars, and Engines, ...& how might be best to utilize labor available to build them... and the City of Chicago