The bottom bar was a feature added in the early ALPHA stage. This was the *main menu" of early ALPHA. It was meant to have the shop, and a help section. The bottom bar was able to be accessed by pressing "b" on your keyboard during intermission. This feature never got far into development, and was never worked on until an early build of the menu was made.
This feature was removed because it was replaced by the menu. The menu was a more efficient way of organizing everything, and was a better fit. This was also removed because it was often buggy and there was multiple glitches where players could keep the bottom bar opened and use it later when the game started.