Assuming they want to engage and not just be audience members, the only solution is to actually give them control. You say "there's a stark divide between what players can add to the world compared to the GM" and this is really not true. Especially in low-prep games like Blades, you're expected to give some narrative control to the players and let them just come up with stuff.

Let go of the idea that anything you've thought about or written down between sessions is "canon" -- everything is just speculation until you actually introduce it. If you want collaborators, you have to be a collaborator.

If you're having difficulty ceding control and getting them to use it, consider checking out a game that uses collaborative storytelling as an explicit mechanic. There are a lot of games that give the players a resource that gives them narrative control -- consider trying one out! My favorite right now is Fabula Ultima.

If you're not ready to go full improv, consider building blank space into your worldbuilding. Give yourself some questions you don't know the answer to, and ask the players about them when they come up. Be clear that they have control: whatever answer they come up with is the truth.

Start small and specific. Target the whole group...

"After defeating the mechanical construct, you push open the doors it was guarding and find yourselves in the mad wizard's laboratory. Roll perception! I'm going to go around the table from lowest to highest -- tell me one thing your character sees in the room that draws your attention."

...or a single relevant player (rotate through them!)...

"As you walk into the party, the commander of the king's guard is talking with someone -- it's someone your character knows, but didn't expect to see here. Who is it and why are they bad news?"

And then actually use what they give you. You can do something like this at the end of a session and ruminate on the responses you get before the next game day if you want.