So I've been noticing that whenever I'm around other players that are higher ranked than me, I always lose my squad mates to them. Now, I understand that higher ranked people should be able to take vehicles from me and stuff, but how come whenever I get a squadmate, I lose them to a higher ranked person or the squadmate just leaves me! What's the reason for this? Cause If this was a mechanic that I didn't know about, Im seriously confused about this.

This is your point of view and that's only half the truth.
Apparently you don't know that a higher ranked players also can lose their squadmates if there are other players around them with no squad members.

BTW this matter already been discussed here

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"Ad cogitandum et agendum homo natus es"

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Ah. That sucks. But I guess it's fair. Still irks me that you can lose your squaddies if someone doesn't have any.