So why do people tell you that they care and then turn around in act like they don't I'm so puzzled about this and just don't know what to think

Lots of reasons.
Such as:
1. They lied.

2. They cared to a certain degree, but then figured out a much greater degree of caring was required, and that was more than they were willing to care.

3. There may be expectations associated or engendered by stating they care, but they're not willing to assume or live up to or accept those expectations, they're only willing to care and behave like they care according to how they wish to express it.

4. Could be simple miscommunication. They say they care, and do, but how you or the other person understands "caring" and its expression is different. The person that said they care may not realize they're acting like they don't care.

5. Maybe they don't "really" or "truly" understand what "care" means. They think they do, so they say it, but they have no idea how to back up what they said.

6. They cared at the time they said it, things changed, they stopped caring.