It is usually because the design is some PM's means of getting promoted. It wouldn't look good if your work gets trashed. So it gets pushed all the way through and then they leave for greener pastures by touting the work they have done.

Someone else gets to reap the damage they have sown. But engineers do the same thing.

In this case, Snapchat just seems to be copying feeds to make money. And Wall Street is breathing down their necks.