Right, choose your own and MUDs and such are environments created for you with pre-determined options. I play those, sure, but the pull of tabletop games for me is the creative aspect. Creating a character (in the senses of 'fictional character' as much as a stats sheet) as a player, or a world and (npc) characters to inhabit it, as a GM. These more freeform approaches to solo play open up a lot of scope for individual creative exploration, and some GMs use them to help develop a setting they later go on to use in a group game.