Town Portals and disconnects

This is not a suggestion, or a complaint, so I hope no one interprets it as such. Just a curiosity.

It's an issue that very rarely affects gameplay, if at all. If I disconnect, why can't a town portal that I previously created persist through that?

It just seems odd, considering random loot in a randomly generated map and the uncovering of said map can be saved through logging off/disconnecting.

Is there some exploit that would be possible that I don't know about if TP's weren't taken away upon logging out?

Thanks in advance if any info is provided.