After meeting someone in here, why leave Reddit dm chat to have conversation on another platform?

I met someone on here a few month's ago and they dm me. After brief back and forth she ask me to go over to google chat. We chat there for few days when things just didn't seem right,and everything about it was screaming "scam".(I ended that chat). I met a couple more people that I just stayed chatting in dm and felt fine about it. Now today I meet someone in dm that sounds almost too interesting and they wanna move to different platform after a few texts. Do I just have "ptsd" or is moving to different platform typical?