He used to be used more: When Zenyatta was dominant in beta (and didn't require LoS for harmony orbs), so were Genji and Tracer. He dropped to being "balanced" at launch, in the sense that he was used about one-third to one-half of the time... until the McCree/Widow nerfs.
Those nerfs indirectly empowered tanks and other characters that Genji is at best neutral with, especially Reaper and Pharah, both of whom have seen much more use since the patch. Reaper is, honestly, overpowered at this point, but it'll take people a while to figure that out fully. He was strong before, and now McCree isn't a reliable counter. Reaper's also more necessary than before now that it's safer to play tanks. Pharah's in a good spot (and a good Reaper counter!), but in the hands of a skilled player, she's bad news for Genji.
So Genji is getting edged out of the meta not because he sucks, but because he's not a good counter to the heroes that are currently optimal.
This is all an indirect consequence of them choosing the wrong nerf for McCree (nerfing FtH's damage instead of its availability). Good Reapers can now routinely escape FtH, which is bad news.
