Hand suggestions are ordered based on the hands that are statistically most likely to be successful - not simply the number of tiles you currently hold toward a particular hand.
For example, you might have 8 tiles toward one hand, but still be missing two difficult pairs. At the same time, you may have 7 tiles toward another hand where the key pairs are already in place. In that case, the second hand is actually more achievable and would be ranked higher.
The system takes multiple factors into account, including the difficulty of completing singles and pairs, whether a hand is concealed, your progress toward pungs and kongs, and more. It’s designed to go beyond simple tile counting, which would often lead to less effective recommendations. Because of this, suggestions are continuously recalculated as the game progresses and new information becomes available.
This means hands may move up or down the list, appear, or disappear as the relative likelihoods change. That said, if you’ve chosen a hand you’d prefer to play, you’re always welcome to follow your own strategy and close the suggestions at any time.