Well...this is an army builder program.
Everybody is waiting for the official designs to be loaded into it.
Now I'm happy as the next person to see an official dataset, but it takes time. And as noted by some above, they are waiting to buy it until it includes certain datasets.
If the program were to load designs from the most used designers out there, it would allow people to play (with unofficial and unverified files of course) in whatever era they want.
Also, I like the printouts of this program. They look really good. I would like to play with the printouts of this program. But right now I would need to play with some cards from this program, some cards from the MUL, some cards from other programs, and some cards that I generated myself because NO programs generate them. The mix of cards from different sources makes the game look less professional when played in public.
And finally, we know from experience that one of the greatest draws of BattleTech is its support for custom designs and refits. Since computers became big, the most popular programs have been BattleMech designers. Were Army Builder to draw on that popularity I am rather certain it would broaden the appeal of the program.