It's not a matter of losing a 100 dollar airplane. It's a problem with losing 5 or 6 a match AND not being able to rebuild before the next match. Most people have a life that doesn't include rebuilding all the time. Combat goes in waves, folks live with the rebuild time for the excitment of the match, for a while. Then they move onto other activities that are less destructive until they get the itch again.
Foamy combats are great in that they can be flown close in, generally use about a bucks worth of foam with 60 bucks of equipment which has seen many airframes. Good flying foam ships fly acceptably nice though they are slow.
B-17's wouldn't work so hot unless you want a B-17 profile with a single motor up front. Otherwise you're looking at 2 or 4 planes worth of motors, esc's for a single event. And watching a b-17 in a furball would be just, wrong.