Keep in mind that the time that your flight is scheduled to land and the time it actually lands can be two very different things. Flight delays and cancellations can be due to weather, mechanical problems, unavailable aircraft at your departure airport (because the flight has not arrived from wherever it's coming from), and even missing crew. I've had numerous delays of over four hours, over the years. It's even worse with connections.
If you're going to WDW, and your flight arrives 5 hours late at MCO, you just get to your hotel later -- and you've wasted part of a day.
But if you're going in a cruise and your flight arrives 5 hours late at MCO, you'll probably have to figure out how to join the cruise at the your ship's first foreign port. (That's Tuesday if you're on a 7-night Disney Magic Saturday departure.)
But even if someone could guarantee an on-time flight, I'd still rather fly in the previous day. It's much nicer to start the cruise relaxed and awake.