However, in almost all newly designed Google apps that still retain the drawer it relegated to act as second level navigation containing less important, more rarely needed functions.
The bottom navigation is highly visible, usable, discoverable and reachable but it has a serious downside: you can realistically have only up to 4 to 5 items on it. Anything more would make the navigation difficult to use and awkward. The drawer, on the other hand, provides nearly infinite extendability. When you add a new feature you can simply add a new line to your drawer and you’re set (none of your users will find out about the new feature though).
The combination of bottom navigation and the drawer seems to be the optimum solution to both, discovery and extendability.. at least until we figure out something better.