So according to the link Jeff passed. At first, the .COM beat out a new gTLD domain name when it came to quality traffic: but .COM traffic was more expensive in exchange. However, that changed one year and four months later.
Back in May 2014, They found that domains of new extensions were converting at about 34 percent, and .COMs were converting at about 52 percent. Therefore It cost more to advertise using a .COM than a new domain extension. However, over a year and a half later, new domain extensions are converting at about the same rate. And .COM domains are converting now at nearly 20 percent. Still costs more to advertise using a .COM domain name than usig other though.
Probably the .COM stale expensive cost caused this sudden shift and increased convertion rate.