Why does a small soap bubble floating in still air become nearly spherical?

Answer: Its film shrinks toward the smallest area enclosing the trapped air

Its soap molecules link into rigid circular hoops — Soap molecules do not build rigid hoops that hold the bubble round. They help form a flexible liquid film, whose surface tension favors a sphere for the enclosed volume.

Its film shrinks toward the smallest area enclosing the trapped air ✓ — The film pulls inward through surface tension, and a sphere encloses a given volume with the least surface area. Reducing that area lowers the film’s surface energy. Gravity and outside forces can distort real bubbles, so the spherical shape is an approximation.

Air currents smooth its surface into a ball — Air currents can distort a bubble rather than make it round. A small bubble becomes nearly spherical even in still air because its film tends to reduce its surface area.