They did.
Honestly, I don't think they should have – the horse is likely to be recaptured and used again. But I'm not surprised they didn't want to kill an innocent animal.
I've met a lot of Ukrainian soldiers. I've yet to meet one who actually wants to be doing their job. They all want Russia to be defeated as quickly as possible, so they can go on with their regular lives. That said, the peace needs to be real and durable. A bullshit ceasefire will not achieve that. Destroying Russia will.