Why did the House pass the DARK act?

Recently at Senator Casey's office, we had been receiving a lot of mail regarding the DARK Act, which is H.R. 1599, an act that essentially bans the requirement of GMO labeling by companies on any of the food products that we as citizens would consume. After the passing of this act, many people were outraged. According to surveys done in 6 key states, 9 out of 10 Americans wanted the DARK act rejected. (http://www.ewg.org/release/voters-six-key-states-overwhelmingly-favor-mandatory-gmo-food-labeling) I decided to look into this act to see what potential reasons the house would have passed an act that was so deeply discouraged by constituents all across America.

It is possible that members of the house that voted for this act (which the majority of were republican, however some "farm state"democrats voted for it as well) could have believed that their constituents were not well enough informed, believing in "myths" over GMO labeling, like that it would increase the cost of food or that GMO labeling that is voluntary will work just fine (when in reality, voluntary GMO labeling has created a ton of confusion among consumers). I found it extremely interesting when I read that many other nations, including Russia, and the EU make it mandatory to label GMO's in food. Some articles argued that the house was greatly supported by corporations, and that the house may have passed this act in order to protect those interests. Now, citizens and constituents all over the country are pleading with their Senators NOT to support the act, which is a prime example of the checks and balances a bicameral congress can provide, as many citizens clearly did not want this bill to pass, and now by consulting with their senators, have a good chance of defeating it.

Many of the opponents of the bill are Democrats, and because of the majority of support coming from the GOP, could this split and support versus opposition be another example of the incredible separation that is in congress today? Several blue states have already passed laws requiring the labeling of food, and many others (including swing states) have at least proposed legislation that would require it as well. Of the states that have not done either of these things, they are consistently red states. Could that be an example of constituents and state legislation standing by their representatives in the senate and in the house?

http://ecowatch.com/2015/07/23/gmo-labeling-dark-act/
http://www.justlabelit.org/dark-act/
https://www.congress.gov/bill/114th-congress/house-bill/1599
http://ecowatch.com/2015/07/24/house-passes-dark-act/2/