NIntegrate owns the attribute HoldAll:

Attributes@NIntegrate
(* {HoldAll, Protected} *)

However, when reading this answer, I surprisingly noticed that at least in the following case the 1st argument of NIntegrate is actually evaluated!:

NIntegrate[BesselJ[9/2, x], {x, 1, 2}] // Trace

So my question is, does NIntegrate always evaluates its 1st argument? If the answer is Yes, what's the meaning of this design, why not simply use HoldRest?