It's likely not your spend. It's the freight forwarder's spend.

I used to work in the industry and I posed this question many times. I was told that, as a freight forwarder, if we spent a LOT with one single provider they might...just might, throw in a few free flights here and there. But that was the exception.

There's often no shortage of cargo for airlines. Freight forwarders need airlines more than airlines need freight forwarders, and over the Christmas period they often reject freight as demand severely outstrips supply. I never felt we were valued by any particular carrier. It was more of "Ugh, if you're giving us money to do it we'll move this freight when we have time I guess."