A Walton Family Foundation spokesperson provided a statement explaining that its grant “supports work to highlight initiatives connecting young people to careers and jobs earlier in their K-12 schooling experience.”
Because they know that "progressive" has a nice ring to it that makes it pretty plain what the associated values are. Everyone understands what "progress" means, and it's generally got a positive connotation.
But "liberal" sounds like someone who abuses their freedom overmuch. It has been turned into a dirty word.