It's quite uncommon for an Aries to first desire a committed partnership. Aries are more likely to fall for the "just for now" pleasure in a relationship because of their impulsivity and eagerness to try new things in life.
They may occasionally find long-term relationships to be a little too demanding, so they prefer to stay away from them. These are the kind of people who live a fast-paced life without being restrained by emotions or interpersonal obligations.
Gemini is a sign that emphasises the novel and the novelly fresh. This sign prefers relationships that are short-lived and keep them focused on the present. They want their spouses to bring novel experiences into their life on a regular basis.
Since they wouldn't want to take a chance on a spouse who would make their relationship dull after a time, they do not believe in long-term commitment.
Sagittarians are the zodiac sign's true free spirits. They are driven by a need for mind-expanding experiences, hence they are unable to remain still.
As an independent and adventurous sign, Sagittarius people may not be as interested in long-term, committed partnerships.
They only fall in love with somebody in the here and now for a certain purpose, and if they realise it's getting boring, they'd rather move on.