My understanding is that it suppresses inflammation. Inflammation is what creates the pressure and the corrosive exudate that lets the abscess push/eat its way through to the outside. If you stop it, you risk it taking much longer for the abscess to mature enough to resolve itself.
Danilon is an anti-inflammatory, so stops the abscess coming to a head, which it needs to do in order to get rid of the 'poison'/infected material. Vet insisted on giving my mare bute when she had a persistent/recurrent abscess (vet was actually here for something else). It only cleared up properly when the Prascend kicked in.
My mare has Danilon for arthritis, I was in a quandary what to do so did drop the dose slightly but I checked with the vet and she reassured me that it wouldn't stop the abscess and sure enough it erupted out of her coronet band a few days later. The vet had never heard of the thought that Danilon/Bute would prevent the abcess processing but did agree antibiotics could.
Yes, I had this back in the summer. He was lame, but not that much really. It went on and on, again. And on, and on. Vet did give antibiotics on the second visit, a week after the first, but this did have the effect of "concentrating" the infection, which was coming through the coronet band, where I was poulticing, but when the farrier came he cut a wedge into the side of the hoof wall at the bottom. I have never had so much gunk come out of a hoof before, but once it started it cleared up quite quickly, so I guess the vet was right this time!
My friends horse had a hoof abscess, started Jan 2020 and he had it for 3 months - then, a very recommended she stop giving him the Danilon for the reasons mentioned above, and low and behold, it came out within a few days. My boy has had an abcess since Christmas Eve, off-hind; - vet has seen him, pared away , located and drained the abscess, under sedation, and put him on Danilon; problem I have is he has shivers so I cannot tub his foot in warm water and salts, and he is still struggling with the foot, shivering away. The bruising is appalling too. Shivers is just the most awful thing, but combined with a hind hoof abscess it is horrendous. I feel so sorry for him.
I've always been told to NOT give anti inflammatories for an abscess as it makes the body try and fight it rather than get rid of it and makes it end up lasting longer.