Why do people say true love or finding a soulmate is rare when most people are already in relationships?

[Anonymous]

If you are already in a relationship or had past relationships, wasn't that another person your soulmate or true love. Maybe something happen later but since you were with that person, they were the person for you?
If not how do you differentiate just relationships and true relationships?

[FictionalCharacter]

In my long distance relationship. I don’t know if my boyfriend is truly my soulmate. I’m trying to make it work. But there is strain on our relationship cause of different culture and different time zones, along with my insecurities.

[scott04sa22]

My soulmate is happily married to someone else. Single for life