Because the maker didn't intend for 2nd flag to be so easy to get to.
In the beginning, you basically went around main all the way through the halls.. Then people thought to pile up on eachother and boost into bd.. Now you can just fly in without thinking about it. It's better though. You have to have a much stronger defence now to watch both flags while the other team has so many ways to grab. (bd to flag 2, water/doors to flag 1, backdoor 2 to flag 1)
Without bd, it's basically a 1 path map. You have to travel through thin halls to flag.