Probably simply the same reason 1 and 4 on the 380 don't have reverse thrust - they have more engine overhang than any other commercial craft except the Antonov Mryia or Spruce Goose.
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....it wont do them any good being started up then immediately being poked up to takeoff power without a warm up.
Yep - which is why they
aren't started up then immediately poked to takeoff power. You sit there occupying the runway until they have warmed up - or:
Alternatively in order to minimize RWY occupancy, (emphasis added) engines 1 and 4 should be started up on TWY D facing south,...... etc.