Stairs manufacturer sells us a stairs to the roof outside but then can't install it "you only bought the stairs"

We wanted to get a stairs from our side roof to the main roof.

So we hired a stairs manufacturer guy. His stairs look great so he came to measure, designed us one, built it. All good. Great guy.

Then the time comes to install the stairs.

He tells us “You need to find someone to install the stairs”.

I spit out my hot chocolate, “Wait, you can’t install it?”.

“No we only design and build the stairs, you need to find someone to install it.”

Me: “Do you know anyone?”

He: “No, it’s very difficult to find people to install it”

Me: “So why did you sell me a stairs if you know you can’t install it?”

He: “Hmmm difficil”