Higher fps broadcasts are a really neat idea and one of the reasons during CSGO majors why I choose to have the GOTV on one monitor and the broadcast on another. It also seems like a super neat way to try and innovate something like a VR esports viewing experience. However, due to the current limitations on bitrate, lack of support with most browsers, and the pretty niche viewer market/lack of demand I can see why it's just not a viable option at the moment, especially with the increased bandwidth/network overhead required to have something that looks just as presentable as 1080p60 max bitrate.
I really hope in the future innovations can be made to make 120fps more accessible (i.e. higher bitrate caps, changes to player to make it work outside of chrome?) because it's a really neat concept especially for FPS games broadcasts like CS, VLR, TF2, etc..