According to Education, gravity affects the shape of soap bubbles by dragging them towards the ground. The site notes that gravity also affects the overall fragility of the soap bubble.
Education notes that soap bubbles are formed by the combination of water and soap molecules stretching around air. Without gravity, the shape of the soap bubble would be determined by air alone. However, gravitational force gently pulls the soap bubble downwards, which gives the bubble a slight point at the bottom. Gravity pulls down on the molecules forming the thin film of the bubble. This causes the skin of the bubble to become increasingly thinner at the top, eventually causing the bubble to break. Gravity also shapes the direction of excess moisture from the bubble and causes the extra liquid to collect at the lowest point and drip off.
To demonstrate the effect of gravity on bubble shape, Education suggests quickly pulling a spool from a soap container. Notice the different shapes created by using different levels of speed, which effectively increases the amount of G-force on the bubble. According to Education, soap bubbles are like any other spherical object on Earth in that the gravity of the planet makes it difficult, if not impossible, to make them completely round.