Why? Campaign contributions/lobbying/bribery. Whatever it's called in your particular jurisdiction.
Rushing or backdooring these things through has a cost, and a price. Both have to be higher than a normal legislative process, I believe. I guess I should say "what motivates people to rush or backdoor these things through at the higher cost?" rather than just say "Why?".
The reason to do it under urgency is that it's so incredibly flawed and unpopular, it probably wouldn't stand up to a normal democratic process. So by sidestepping the democratic process, it makes it much easier to get things done.