Even at the peak of my Overwatch playing spree, I always found Overwatch boring to... Watch. Too much going on, and if the casters were focusing on one person it was dull.
It's like, when you watch a MOBA, there's an ebb and flow to calm periods and to the fights and things are happening mostly in one screen and people who are fighting are right on top of each other. In Overwatch, it's disjointed bodies shooting at each other and blocking with shields and turning to shoot other disjointed bodies with a single flick of the mouse because shields are there. And it's non-stop. Someone is ALWAYS in a clash, and is ALWAYS doing it at whole-room scale. When people had ultimates to break a choke, it suddenly became better, but the whole in-between was just nothing. Noise. And even then, ultimates like Lucio's or Moira's later on could easily cause the big issue of "The blob". Like a cartoon fight with smoke, where details don't matter, someone sometimes can be seen choking someone else or biting their own leg, and in the end someone comes out victorious and who knows or cares why. I've only ever seen one game try and do worse, and it's Splatoon. And by try, I don't actually mean they tried much at all. But OW did.
And it wasn't a shooter problem. Counter-Strike has such low TTK that when a clash happens, you can generally get the camera focused on those people and lose nothing of importance elsewhere. All the nitty gritty of a single round can be understood in a single, real-time watch. I couldn't with overwatch because there were just that many people always in the heat and the important play could happen ANYWHERE.