If you ask why we don't have over 7000 functions listed there, the answer is easy: It would be a nightmare for you to use.
Recently I made a special version of MBS Plugin to register all functions individually and show them in the calculation dialog right away:
You don't see the scrollbar on the screenshot, but all 7000 functions are there. The dialog takes about 12 seconds to open as FileMaker adds all the functions to the list. And it takes another 10 seconds to open the MBS section there. There is a significant time cost for having a lot of functions there and thus we don't do this normally.
Please pass the function name to MBS() as first parameter to pick the function. Take benefit from being able to pick a function name from a field or calculation.