It's probably easier to bring the troops to the set up training infrastructure than to take the infrastructure to the troops, remember some of the things involved are the likes of the urban / combat village set up that the UK has for training troops in house to house combat and the military driving ranges to teach them on the vehicles provided.. you can possibly deliver them to the UK on the probably empty return aid and munitions delivery flights.
It also brings them together out of area and lets them knit as a team as well as being a huge moral boost for some of them that will never have been abroad as such?
North Macedonia is providing 4 SU25's they have in store, well done for such a small Country.
https://www.kyivpost.com/ukraine-pol...u-25-jets.html