Ostensibly, they made the security increases in iOS to prevent from being able to comply with these types of requests, ensuring that their software was as secure as possible.

Aside from that, a fourth amendment search or seizure cannot generally compel someone to open a door. The usual logic is that it allows agents entry; the trade-off of letting them in is that you don't have to replace your door after.

This isn't a matter of standing aside while the agents effect the search, it's a whole different thing. Put into (what will assuredly be a bad) analogy, whereas a physical property search involves opening a door, or standing aside while the cops break down the door, this scenario is more akin to demanding that Apple build an entirely new house, one without doors, then removing the old building and installing the new building in its place so that the cops can enter.