Good question! It's hard to say why the chicken didn't go down the slide. It could be a few potential reasons:
Fear - Chickens, like many animals, can be timid and scared of new environments and things. Going down a slide, even a very small one, could have been a bit too much for the chicken in this case.
Not knowing what a slide does - Chickens have a much different view of the world than we do. So, it's possible the chicken just wasn't familiar with the concept of what a slide does and why it would be fun to go down.
Not enough motivation or incentive - Perhaps the chicken did not have enough reason or incentive to go down the slide. As you may know, chickens aren't typically interested in thrill or adventure. Unless they were offered something they really wanted, they may not have been motivated to give the slide a try.
Ultimately, it's hard to say why the chicken didn't go down the slide. But perhaps it was a combination of all three of the factors mentioned above, or something else entirely. If you ever have the chance to try putting a chicken down a slide again, it could be an interesting experiment to explore their response!