"We all find our comforts in different places. This is a home away from home for me. I'm sure you have your reasons for wanting to stay where you are - but like I said, so long as you're happy with where you are, who you're with and what you're doing, there's no need for change."
The Greeks in general didn't tend to excel in parenting. Poseidon knew that he tended to leave his kids to do as they pleased - not because he didn't care but he thought it would be better for them to learn about life the way they wanted to. Just because the time and the place they are in now is so different to the past didn't mean that Poseidon was about to start interfering with everyone's lives and tell them what to do.
"But since you're here, stay as long as you like. There aren't a hundred places to visit or things to do, but there's water." And the fact that there was water was in itself a hundred good reasons to want to stick around just a little bit longer.