Why sukha (third Jhana) is more refine than pīti (second Jhana)? Why is sukha (third Jhana) higher than pīti (second Jhana)? In other words, why does sukha not come before pīti?

This question is based on the following suttas in the Moggallāna Saṃyutta.
Lesser khandha = Stable mind state = Better happiness.

Vitakka, vicāra, pīti, and sukkha are acceleration of consciousness to access jhāna. the practitioner need them to develop jhāna-consciousness, until he turn to be professor in each jhāna. After that they become an obstruction of jhāna's stability.

Too many cooks spoil the broth.