Because if you've already been accepted into the new one then at that point in time you're in TWO legions at the same time!

It should not be difficult for a developer to delete any old Legion from the respective player database and insert the newly joined Legion upon acceptance.

This would simply be a waste of Dan's time, if you dont want legion down time ask the people you want to join ahead of time.

You can have requested to be in many groups at once and they might accept you in any order. You can't unsend a join request and the group leader will only know if it is still a valid request by clicking "accept". It could work id there were only one request per player at a time.

On a side note, I thought it might be nice to be able to see new requests even if a group is full. I would probably only kick the lowest level if the person wanting to join was rather freakishly high-level, but it would be nice to not have to be paranoid about actually having the group full.

I don't really know exactly how sharing works when someone changes legions, but I bet there is something that should be fixed with that.