Meter building builds different kinds of games as well. I would argue you get a bit more variety in combos/strategies when you can keep your meter as if the game allows for it, you can give up the first round to build meter to go bat crazy in the second round for the momentum or in general you just get to see more variety in terms of meter usage. In games like GG/BB/ST, anything you see can be seen in every round which can or won’t be a good thing. As a spectator sport, you want people to see new stuff more consistently and if you see the same amazing combo every round because it’s possible, it stops being amazing.
Of course really it comes down to a preference and a game doesn’t HAVE to have one or the other. It would change the game if we were to say allow people to carry over meter in ST, but I don’t really think either are all that bad, rather just what you like.