It is true, all of these rubbish being left behind by climbers. But they pay a premium price for the climb. Everest permits are $ 11,000 from Nepal or 9500 from Tibet (china) . There is a (refundable) Trash deposit and other costs are totalled around 9000, on top of the permit fee. Nepalese government simply issuing those permits, and collect the money. This is not like climbing Hantana or Samanala Kanda. This is the ultimate climb which kills roughly 8-9% of climbers.
Nepalese government must take responsibility for the cleaning up, because they are the ones who allow all these people to carry those disposable stuff (without those, there won't be any climbers)and charge money for the clean up.