One game? Are you taking the piss? What about the fact that the crowds to the international T20 matches at the MCG have also been huge in the past few years. Last night was hardly a once off! And it's about to be topped tomorrow night. These games are rip-roaring successes.
Apart from anything else, international T20's give more a chance to shine for their countries. If it was all the same old same old's playing all three forms, you could get a bit bored of it, or you could argue it's "pointless", but this gives those who are better suited to the shortest form a chance to do their thing.
It also gives those that are getting on a bit, but who still have good skills (but not the fitness or desire to play the long forms any more) the chance to keep on shining. Like Hogg, who did very well last night and will probably do even better on the spinning pitches in the T20 world cup.
Again, anyone who doesn't like it doesn't have to watch it.
But plenty obviously do, so it's for them, not those who aren't interested.