Indeed, these were a luxury ride for company heads...
But back in the day, it was either that, ride coach or caboose, or take the stage coach. The business car provided food, lodging, and transportation to anywhere on the line, and you could go schmooze some mine owner, cattle baron, lumberman, etc. anywhere- which was a lot in the west in 1890. No depending on local eateries or lodging- if there was any. One could work in an office in the evening, and not have rif-raff at the bar downstairs making noise.
While lavish, it was also a mobile business office before highways, hotel internet, etc. You could go anywhere your business did!
I get what it was, when it was. And there is no question why usage fell off as soon as the automobile made inroads into narrow gauge country.