Floor under shower not insulated.

[Funny1]

So I just took the cover off at the bottom of the corner shower to see if there are any leak issues and it all looks nice and dry, BUT I noticed a cutout under the shower drain for whatever reason without any insulation. This normal? Wouldn't you think they throw some batting in there? Anyhow I was also curious what the measurements of the sandwiched floor was like and what I think I see is styrofoam sandwiched between a layer of 1/4' plywood floor and maybe a 1/8" bottom layer. No wonder these floors become soft in high traffic areas by 200lb+ users......