I don’t know what to say. Well I do, but it’s not polite. 
“No fat chicks!”
That is how they do it now.
Thanks to improvements in technology caulk is strong as steel and no other support is needed so those must be temporary 2x4’s used to hold the spa tub in place as the caulk hardens up.
Product sold at Home Depot is called Tub Support
Do they sell a warranty(extra charge) with that product? 
Not sure but saw Obama had awarded the developer with a special "Green Science Award "as less wood is need in construction.
The contractor will be filling the void with structural foam any time now.
2003 build.
Unfinished area was apparently finished by the home owner.