Simple but I will also say it's speculation,
The locomotives at DL have not been to a steam locomotive overhaul facility in decades yes they have been lovingly maintained but I'm guessing here but I believe (please correct me if i'm wrong) since the 90's, Steamers are so complex they are almost alive and they have high pressure steam, huge rotating masses and huge reciprocating rods and miles of high pressure piping all of which needs to be periodically refreshed.
TRON ain't happening for who knows how long but long enough to require that the existing construction be sealed which is very expensive and is usually done for construction halts of 2 or more years if it were only for 6-18 months the standard Florida construction protection against rain and wind would be sufficient. Without a completed TRON there is not a complete loop for the train to operate over.
So If you are a corporate asset manager what would YOU do ? let the freshly overhauled locomotives rot in a storage yard (because the steel used in steam locomotives corrode rapidly when not at operating temperatures) or would you send them to your other site which is in need of some refreshed motive power.
As to shipping them to the other coast, It's just additional fuel and mileage for the truck(s) shipping them. And as to narrow gauge steam all the repair shops are on the east coast with the exception of D&RG Railway but they don't contract out repairs.