We had the same type of experience while going through the loading area of HM at the MK. There were Kleenexes and food wrappers and general trash lining the walkway (where you get on the doombuggies). It was very noticeable and filthy.
We were at WDW for 10 days, and every time we road HM, it was this way.
I was upset about this "lack of show", and wrote to WDW guest services. They contacted me and told me the CM's of the attraction are responsible for keeping these areas of the ride clean. They apologized and said the proper managers would be notified.
I'm happy to say that I have not seen that level of trash on HM since. I know people can drop things occasionally, but this was an accumulation of trash that had been neglected by the CM's.
So, letting WDW know about these things does help, IMO.