You're asking the wrong question.
The question should be, "Is there a reason to use Minnie Van rather than regular Lyft?"
As PP mentioned, some people use Minnie Van because it has 2 car seats. Some people like the idea that the drivers are Disney cast members.
But the biggest reason is that a Minnie Van can take you places on Disney property that a regular Lyft cannot. For many people, that's getting dropped off at the Magic Kingdom; a regular Lyft will drop you off at the Transportation & Ticket Center.
But for other people, it's knowing that they will be able to get past the guard at a hotel. The guards at the gates of some hotels will not let a regular Uber/Lyft in unless the passenger has a hotel reservation or a restaurant reservation. Too many people were getting dropped off at hotels near theme parks (think Contemporary or Beach Club) and walking from there.
You asked about Topolino's, which is at Riviera Resort. I haven't heard specific reports of guards at the gate of that hotel turning away people in regular Uber/Lyfts, but I don't spend time at Riviera so I wouldn't have been paying attention.