Maybe a fuel issue. Perhaps Uber is paying the helicopter company extra to compensate for the increase fuel burned from its customer's heavier luggage. That's one way to set yourself apart in the market.
Uber probably just rand the numbers and figured out that everything over 28lb or something is a rare outlier so allowing 50lb makes for better marketing but costs little more than say 30lb. 50lb is decently heavy. The intersection of "people willing to pay $200 for a helicopter to save time" and "people willing to lug around 50lb" is probably reserved for a handful of specialized repair technicians (like the kind you fly out to somewhere) who carry specialty tools and expense the cost, a rounding error in any case.
