The Pad Bank buttons on virtually all MIDI controllers, together with buttons like Note Repeat, Full Level, Half Level, and 16 Level, are controls that operate the MIDI device's internal hardware; they do not send MIDI data to your computer.
For example, the MPK Mini already has the Full Level feature built in, so you don't need a Full Level software button for it. Similarly, if your controller already has a Pad Bank hardware button and can internally shift the MIDI data it sends to match a higher or lower pad group on your screen, you don't need a Pad Bank software button.
In the event that the MIDI device you're using lacks hardware buttons, the MPC desktop program will compensate for this by allowing you to add the buttons directly through the software using advanced MIDI programming. In this instance, mapping a function to your chosen button would be accomplished by using the LEARN button from within the MIDI Learn panel.
The MIDI Learn panel can be opened by pressing CTRL + Shift + L for Windows, or Command + Shift + L for MacOS. You can also follow the gif below.
To summarize, if your controller already has dedicated hardware buttons for any function listed under Pad Bank and Pad Panel, it does not need to be mapped to a software button.
If your controller has no dedicated hardware buttons, you have the option to map a function to a button of your choice directly within the software.
In the event that your controller has a pre-configured mapping within MPC and the Pad Bank and Pad Panel options are grayed out, it indicates that your controller already has dedicated buttons for these functions, so software buttons were not configured during the mapping process.