It's the kitchen.
I'd try anything to break the black up tbh...a few pictures/photos on the fridge...a fruit bowl on the work top...a couple of cutting boards laid flat/leaning on the back...flowers...tea towels over the drawer handles, maybe even a splash back?
It might not make any difference, but it's worth a try.
I'd spend as much money as I could afford on nice pots & some colourful plants to fill them & arrange them altogether in a group. You can shift these around for the photos, so it looks like there are more!
I'd take the photo of the garden from the conservatory off the website altogether.
If the kitchen hasn't put people off, the fact the garden is so overlooked might prevent people from wanting to view.
Is it worth moving the garden table away from the fence a little bit? I think it might actually make the garden look bigger and more usable. Furniture generally gives the impression of there being less space when it is squashed up against a wall, so maybe worth a try?
Good luck!