I thought it was cute too, thanks.
Most of the serious discussion goes on elsewhere, but reasoning for team attack off:
1. Broken/ridiculously annoying strategies
These are incredibly common. Two Falco's spamming blasters? A DK spamming down+b with an MK spamming tornado or a ROB shooting lasers and gyros? D3 throwing out random forward smashes while his Snake teammate goes ballistic with tilts?
None of these really showcase skill, but rather a pre-determined strategy that has very littler variance to it.
2. Ease of play
Team Attack off = easy. You pick it up, you play, and it isn't difficult to imagine scenarios where a more skilled player can be hurt simply because he is forced into a situation he can't do aynthing about because there is no longer any punishment. With team attack on, you can't whiff an f-smash at will, knowing your teammate will be there to cover you up. It takes better thought, spacing, and planning... on everyone's part. Generally, the more complex something is, the larger the skill gap becomes.
3. Spam factor
You should never win by randomly pressing buttons. With team attack off, this is possible because punishment is reduced.
4. History
It has always been on, and no one that plays in tournaments would play with it off... so no TO will leave it off.
5. Insanely altered gameplay
Above all else, it is a
different game with team attack off... just like it is different with items. Tiers are shifted, stages have to be reevaluated, etc., etc.