One of the things Sakurai does is use the reference arts of the Pokemon he gets sent to determine who gets in, he did so with Greninja, before it even had a name. Let's assume he got sent all three, it's obvious why he would choose Incineroar out of the them. For one we have quite a few archers in Smash already, but what we lack is a full blown wrestling character and some new heavies, Incineroar would knock both off the table. Second, Incineroars entire concept art has it show more personality and general action than the other two, this is not saying the others are bad, just that their reference sheets are kind of empty compared to Incineroars. The table slam, the lariat, the way it emotes. Those are all key factors. Now, I'm someone who really hates Incineroar, because it's just fucking ugly and the proportions are ridiculous, but I can see why Sakurai would prefer it.
