Money, need, and variety.
Please bear in mind that the 483 has not steamed in my lifetime. I would love to see 483 working again, but there are plenty of other K36 locomotives in service, both on the C&TS & on the D&S. A coal burning K37 would be a bit more unique. If cost were no object, I'd rather see a K37 in service. Of course, cost is a variable at every step. Would it be easier and cheaper to maintain and run another K36, or would the maintenance, repair, and operation of a K37 be more viable? What would the shop prefer to work on, and what would the crews prefer to run? Is one more efficient to run than the other? Would the possibility of seeing a different class of locomotive in operation attract more riders, and if so, would the novelty wear off?
At this point, I get the impression that the ridership would not require another locomotive anyway (please prove me wrong). As things currently stand, I'm thankful for what we do have and am trying to visit and ride every year. If another class of locomotive goes online, I'd be thrilled, but I am in no way unhappy with the current arrangement.
Dave