One of my theories is that TV really doesn’t even need play-by-plays, especially nowadays with graphics giving you so much information. It’s a medium for analysis.
Conversely, I believe analysts are superfluous and possibly even detrimental on radio, which is much more of a medium for play-by-play description. I love listening to old Ernie/Paul broadcasts, where for the most part it’s just one guy talking during his innings. That way they could concentrate on keeping the listener apprised of what was happening instead of trying to maintain a conversation. It also allowed the broadcasts to breathe much more; during lulls in the action they’d lay back and just let you enjoy the sounds of the ballpark.