There are certain types of outboard motors that just work best with specific types of oil since outboard manufacturers typically will create oil that is built for the outboards that they produce. Since they have the best understanding of how their own motors work, they are most qualified to create oil that will make them run the best. In some cases, motors even run more efficiently this way.
When I bought a Mercury outboard, I looked into the idea of also buying Mercury oil since I knew that these would pair well. I decided to start my boat out using this type of oil to see if it would be a good oil to use. I was very impressed with the way that the Mercury 2 cycle oil helped my motor run better than it would with anything else.