Firstly, backing out of ED isn’t (and shouldn’t be) common. When a family decides to apply to ED, they sign the agreement saying that they will commit if they’re admitted. Presumably, this is after heavy deliberation involving financials and assurance that they want to attend.
The only time I’ve seen ED backouts is when the financial aid package provided after admission truly isn’t enough, even after appeals and that whole process. Usually, the choice is because there’s no feasible way to attend.
Compared to backing out of an EA admission, you didn’t sign any agreement when you decided to apply to EA, so there’s nothing lost for the University if you ultimately decide to go to another institution. If anything, they get a free $400 from your deposit. You shouldn’t be backing out of an ED admission because you got into somewhere else - they should have applied to that ED school, ED should be for the school you are dead set on attending.
It’s extremely unethical to get admitted ED and essentially ditch the school, and can have ramifications on your other applications or admission offers to other schools.