My guess is because he really does just want one big insane family.  Denise Richards is moving into a home Charlie Sheen purchased earlier this year.  It's 6 houses down the street from him in the gated community he lives in. 
It's really not as insane as it seems (from TMZ)

Our sources say Charlie and Denise are now getting along reasonably well, and Charlie's primary motivation is that he wants to spend more time with their two kids. Some of Denise's stuff has already been moved in, and we're told she and the kids will begin living there in a week or so.

So it's not a matter of getting back together or working things out.  It's about being civil for the sake of the kiddos!  Finally Charlie shows us a spark of sanity!  Welcome back to the real world Mr. Sheen!  We have missed you!