Put simply, it's because you're better off delaying your expenditures as long as possible.
Example: let's say you buy a TV for $1,000. You can pay for it all in cash today, or you can pay for it all in cash a year from now.
If you pay cash today, you spend $1,000. Duh.
If you wait a year from now, you can take that $1,000 you would have spent the day you bought the TV into some form of investment making a 5% return. At the time of the payment being due, you now have $1,050 dollars but your payment is still only $1,000. You walk out $50 richer than if you had just paid cash the day you bought it. Just imagine that on a much, much larger scale.
That's a good example..except...if you are deferring a payment on that TV then you are probably paying a finance charge which will be MUCH higher than the interest you made on investing the $1000 LOL I'm sure that isn't the case with a MLB contract just the geek in me needed to point that out
but that aside....I sort of just think the perception needs to change, I can't name even a handful of contracts which were backloaded that panned out for a team, I'm sure there are more than a few...and the ratio has to be in favor of doing so or why would teams keep doing it? Maybe it's just because the media shows up the ones that don't? ...I'm too lazy to do the work and research it though LOL