A parade of 50 floats would be wretched on guests, park operations, and entertainment. It would be over twice as long as any parade in any Disney park. At the speed Disney typically runs their domestic parades (which is faster than overseas but still surprisingly slow) it would keep guest traffic flows in a knot for over 2 hours. The floats don't typically run up against one another, they have room before and after each float to allow the sound from the various floats to not clash with one another, this would make it even longer. In addition the step off areas (where the parades stage before coming out) are not large enough for that contingent of floats, the parade den is not large enough to store that number of floats. Since before the parade steps off the entire parade has to be assembled, tested, and all performers to places that would also mean that the performers would probably be in costume, in the sun for an hour and a half or more and the float batteries would have to be bolstered quite a bit. And speaking of performers, to keep the quality of the parade up to Disney's standards you would need twice as many of them and all of the costs that suggests. While they certainly could do a 50 float parade if they chose to and I'm sure it would be amazing, unless they spent a lot upgrading facilities, add more performers, and figure out someway not to have non-parade interested guests keep from going nuts it is probably not something they would do.