Question: Why do the Singles & Pairs hands have such a high value?

Answer: Jokerless hands under the Singles and Pairs section of the card have the highest values for obvious reasons:

• You must complete the hand through your own picking except when calling your Mah Jongg tile.
• You cannot use Jokers
• You cannot call a tile for exposure unless it is your last tile which completes a hand for Mah Jongg.

Source:  National Mah Jongg League Bulletin Q&A (1972 page 4)