If you stick to the core 10 disciplines it's 31 latin to 27 ballroom dances so far, which isn't a huge disparity. I think they try to clear the decks of cha cha as early as they can, because it's a pretty boring dance most of the time, and a safe one to give people early over any of the other latins, so that tips the balance in the early weeks to the latin side, with it rebalancing later (there are no more cha chas that can be done this series).
If you expand it and split the other genres (American Smooth and Argentine Tango to ballroom and Charleston and Salsa to Latin) then the obvious issue is that there are just more latin dances in regular rotation early on, because people get very fussy over when the AT can and can't be done, whereas Charleston is really just gooning about with silly faces, and so can be done by anybody at any time. Hence the wider gap - there have been 5 American Smooths vs 4 salsas so far, but 8 Charlestons vs 0 Argentine Tangos.