Why wouldn't it make sense? Obviously if you are an adult and are up at the crack of dawn and can stay in the parks all day, look elsewhere, but for alot of other people who aren't early risers or die-hards, it's not hard to see the appeal.
I can't get my family of 5 to make a 9am rope drop if my life depended on it. Might as well sleep in, perhaps spend the morning in the pool, or a late breakfast at Ohana and stroll on in at 12. I can still get the fastpasses I wanted at 60 days out, be able to choose a new one by 3, and by timing it right with EMH, stay in the Magic Kingdom or Epcot til 11-12 at night. and save a pretty decent amount of money.
Doing the math, on say a day where MK is open 8a-10p with 10p-12a EMH, 2 day regular ticket vs 2 day mid day.
Especially for families with kids who aren't early risers, getting them up at 7 means they're going to want a nap by 3. That means leaving the parks by 2, and MAYBE getting back in by 6? And if you're getting them up at 7 the next day, you won't be able to stay late, so you spend 3 hours in the evening before heading back for the night. You'd be spending 9 hours in the park. Picking a random day in September, a 2 adults and 3 kids would be $1,161.79. That's $64.54 per hour.
If you buy the mid-day, and say just get 8 hours in, 12-8, the total would be $880.32, or $55.02 per hour. And no matter how many hours you get in the parks, it's still a difference of $281. That's two character meals for a family of 5. The savings over a 4 day ticket would be $567.34. That's enough to pay for atleast one direction of flights to Orlando for a family of 5.
My strategy for my upcoming trip is a 1 day ticket for HS so we have enough time for all of Toy Story and Star Wars with a 9pm closing, and a 2-day mid-day ticket for Epcot and MK, timed with the late night EMH days. It's about $170 cheaper than a regular 3 day ticket for my family.