Like every manufacturer, Yamaha realizes that 1) everyone's anatomy - and preferences in a saddle - differs and 2) manufacturing costs are kept down by supplying an OEM saddle that will be "good enough" for the "average" rider - who probably rides < 3,000 miles/year.
It's the same in the bicycle world. So many options available, and so few 'real' riders who keep their original saddle.
So Yamaha - and everyone else - offers a saddle that will work well enough on a test ride. You know, when you're distracted by all of those other attributes of a new bike and probable only giving slight attention to your a$$.
And now, Goldilocks, it's up to you do figure out which aftermarket saddle is "just right".
And then pay until your a$$ hurts!
It's okay - you're worth it.