Without knowing how FTB is programmed, I do know it is a big job to port a program on different platforms (Windows vs IMac OS). It may take a total reprogramming to get it right and that would require 1000s of man hours to do. When that is done, for each change, you need to do the same change for each version.
It is up to MyHeritage to calculate the number of Mac users they will get and then see if it is profitable. So maybe all Mac users should vote for it so their numbers will be known.