There isn't anything in the air for the ukrainians. So they would be only targeting stuff on the ground. Meanwhile the ground will be targeting them. You only have so many flares. So the cost-benefit is probably not there.

Not to mention... how long until a missile tracks something that they arent allowed to shoot. Awful lot of NATO stuff up in the area. 1 nato bird falling from the sky because some newb pilot? You might just find yourself biting off more than you can chew.