Seriously. Each game has introduced at least a few new characters that were never seen before:
Twisted: 18 Volt. He's new, but where did he live before this game?
Touched: Ashley (Mike has an in universe justification)
Smooth Moves: Penny Crygor, Young Cricket and Master Mantis
So... how come we never saw any of them before their first appearances in series? 18 Volt is semi justifiable, but there's no logical reason we wouldn't have seen Ashley and Young Cricket in earlier games. Even their homes look bleedingly obvious on the map screen!
I think it has been said that Mona is good friends with Ashley, so I guess it just took a while for her to convince Ashley to join the group, given how anti-social she is shown to be.
Young Cricket and Master Mantis are travelling for their training, so they were either out of town when Wario created Wario Ware Inc., or they didn't actually live there prior to the events of Smooth Moves.
Can't think of anything good for Penny thought, she does seem to be on good therms with Wario and Do it yourself shows that she is easily more involved in the company than anyone else, so there is really is no (in universe) reason for her to not be there from the start.
Diamond City is full of crazies. You never know when one of them will decide to interact with Wario & co. That, and I like to imagine that the city is never literally seen "as a whole", due to graphical limitations. So there could be more buildings with more crazy dudes somewhere, or you know, they could just have built more crazy buildings recently.
