Hand suggestions are ordered with the best hands at the top, but the hand that is the most likely to be successful is not necessarily the one for which you have the most tiles towards mah jongg.
For instance, let's say you have 8 tiles towards mah jongg in one hand but that hand requires 2 pairs you don't have, and you only have 7 tiles towards another hand, but for this hand you already have your pairs, the latter hand is more likely to be successful than the former so it would appear higher in the list.
So the tool is not just based on tile count. That would be too simplistic and would result in poor recommendations in most cases. Instead, it takes into account the relative difficulty of getting singles/pairs, concealed hands, how close you are to pungs, kongs and a variety of other factors.