Look at things this way William: If you were working on your own personal ride, would you rather do it working in your shed or one-car garage, or would you be more comfortable if you had a nice multi-car garage or even a shop, where everything has a place and you don't have to have everything underfoot?
Now relate that to these teams that are spending 4-6 days a week working on these cars. Yes, you could do it out of a dualie and a Chapparal (take a stroll around the Sportsman pits, or at an IHBA race- most still do there), but given the opportunity (and the moola) to be in a more work-friendly enviorment, you would if you could, even if it was just a single stacker trailer with a well laid out tool box/ work bench configuration.
As some teams have expanded into the "bullet for every pass" mentality, or better, the "we can build EVERYTHING" concept, the need for more efficient and technically advanced trailers/ traveling shops has become a staple. Add in the need to make sure that those that float you the big bucks are well taken care of during race weekend, and hospitality trailers now get thrown in the mix.
I remember when Tommy Ivo used to show up with his glass sided trailer and it would be like the circus just rolled into town.. Now you don't even bring the display car in something that small anymore.