The simple answer is that Dan Jones has more traffic daily. Those traveling to and from Plainfield and Brownsburg make up for a lot of the traffic, in addition to those, like yourself, that travel on Dan Jones from Avon. Yes, during the widening on PHASE 1, you will have to merge back down and go to one lane each way over the bridge... currently. There are four other phases in this project... one of those will be the bridge phase, where the bridge will be modified to match how Dan Jones is being widened. The whole project can't happen simultaneously unless we close Dan Jones completely, which would be worse. As mentioned, many, many times, this is a multi-phased project, and though it's frustrating and rough right now, the way the process is being done is much better than how it could be done.
Side note: Unless you have extremely small planes, I doubt you could get 1 plane on that bridge, let alone two.