I think that John's post said it well, but both think of the times then, and how officials needed to get around, and to show off the railroad to potential investors and such as that. Those were necessary uses for the cars.
Even today, there is no better place to inspect the railroad than from the rear of a business car. Thus, it was not only the highest management that had use of a business car. On many western
railroads (and even some today, UP for example) division superintendents then, and vice presidents today often have their own car assigned to them, just for the purpose of monthly or by monthly inspection tours. Now, even as then, they were the mobile office of the managers and or the owners. Precisely why they were called business cars or office cars.
Was the use of these cars abused? Most probably, but again, the use of the car was one of the perks of the office, and business was expected to be done from the car during the use of it. I recall seeing a photo of a business car set out on a siding next to the river and the officials trout fishing. I am also sure that the car was used to inspect the line on the way up and by a different return
if possible, and the telegraph wire or phone wire was connected to the car, so it was a working vacation.