SEGA explains why Mario and Sonic haven't teamed up for an adventure game, and it's not for a lack of trying

A portion of a SPOnG interview with SEGA’s Osamu Ohashi…

SPOnG: Going back to the first game in the series, when you decided that Mario and Sonic’s collaboration should be in the style of a sports party game… Why did that scenario make sense to you as opposed to a traditional platformer?

Osamu Ohashi: Prior to this project there has always been a discussion between Nintendo and Sega about bringing Sonic and Mario together somehow. But every time we talked about it, there was an issue as to exactly how we could achieve that.

These characters come from two totally different backgrounds, and have completely different worlds. If you do any kind of collaboration, you can’t just get them to run on one of the Sonic stages or vice versa. You have to create something from scratch, a neutral location. Nintendo and SEGA never managed to agree on just where or what kind of universe we could set a Mario and Sonic adventure in.

Then, some time ago, SEGA secured a license to create games based on the Olympics. At that point I came up with the idea of having Mario and Sonic compete with each other in the Olympic games setting. We proposed that idea to Nintendo and they were really positive and interested in the idea, so that is where we started building it into a concrete game proposal.