Why is the new Twitter menu bar on the bottom on iPhone?

Twitter recently released a complete redesign for all major platforms, in part the redesign has been made to unify the experience across platforms.

But, because of this goal I couldn't help noticing the iOS version has the menu/navigation bar at the bottom of the screen:

_{(source: twitter.com)}

The web app's menu is at the top bar:

As is Android's

This difference is easily the most visible difference between the apps and can make the experience slightly confusing when switching between the iOS and other versions. The previous Twitter iOS app had the menu bar at the bottom too.

Why is the menu bar at the bottom on iOS? This visibly harms their cross-platform unification, so there must be some reason beyond "it's the way the old app was" as the apps were all changed despite that.