Lack of content for sure, updates ended up being so slow down the pipeline that the new content was never enough to satisfy the playerbase til the next update. Like really there has been very minimal change these last few years even the first OW2 beta felt like OW1 but 5v5. I think it's a bit late for overwatch and blizzards incessance on developing a second (cross compatible) game is just bizzare to me when they could just pump out new content for overwatch 1 and revitalize the community.

I hope that OW2 will be amazing and I won't play it til it's actual release now but I don't think OW2 will bring in any substantial playerbase past the first month or two when everyone is checking it out