In the history of the franchise, we've only ever had two franchises cut.
One was Ice Climber. We know that the Ice Climbers were supposed to appear in Smash 4 but couldn't due to technical difficulties. They weren't supposed to be cut.
The other was Metal Gear. We don't know why it was cut, but third party legal troubles are likely the reason. We have no reason to believe Snake was intended to be included in Smash 4.
An easy conclusion to take from this is that Sakurai doesn't intend to cut first party franchises. Once they're in, they're in. The far majority of first party IPs included in Smash don't have characters. So the franchises with characters can be seen as essential, either from obvious marketing merits or historical significance. They're special in some way.
So I have to ask, why do people think we're going to lose first party franchises like the retros, Punch Out!!, Wii Fit or ARMS? Sure these franchises aren't as notable as they once were and they aren't a part of Smash's identity like Earthbound or F-Zero. But we don't have precedence that entire first party franchises will be cut out.
We do have precedence for third party franchises being cut. And we do have precedence for supporting cast members of already represented franchises being cut.
But why do people consistently suggest cutting these guys?