Nintendo milks the character Mario but that's about it. They don't milk their franchises but it might seem like it if you just look at the amount of games and ignore that they are spread across several platforms.
Nintendo is in a difficult situation when it comes to their old franchises. The fans expect new entries in their favourite series. I guess Nintendo could stop producing Zelda games but they would get slaughtered for it and whoever made the decision would have to flee to another planet. If they stopped using Mario investors would flee and the company would crash.
It's the Nintendo curse.
It's not like Nintendo never makes new IP's though, but if you want more of them then you'll have to support them. We vote with our money after all.