Well, good question. One of the most common arguments brought up is adherence with the needs of broadcasters. We've added 30 seconds to each half-inning, and that's nearly 10 minutes a game right there. If you have one goal of speeding up the total time of the telecast, and another goal of displaying more ads, that means less baseball. Even with the tweaking at the margins like enforcing allotted time between pitches, that's not a good thing.
Attendance is strong, despite the incessant shrieking from certain ownership fractions.
There's not a business owner out there who wouldn't take flat volume if they could double their prices over a short timespan and control their costs. Longer games mean more opportunities for patrons to purchase items at the concession and souvenir stands, and provide greater value for the advertisers who have purchased space in the ballpark. These things mean more top-line revenue to the ballclub. It may be desirable to shorten games, but I certainly don't see it, at least from MLB's perspective. The ratings for games have not demonstrated growth, but that's a trend throughout mainstream television.