The approach combines the better points of the spread (making the defense account for the whole field) and the I formation (power through numbers up the middle and off tackle).
It's also a reminder the I and the fullback got a bad rap as the era of that style of football wore on. Those offenses became easier to defense after they made the fullback pretty much a sixth lineman, but that era wasn't very long in the grand scheme of things.
Jim Brown was a fullback, after all.
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Woody Hayes used to recruit as many fullbacks and tackles as he could out of high school because those were usually the best players on their teams.
With more ball fakes and backfield action, the T formation also did a better job keeping teams guessing than the 'I' did even though now most people would probably consider the latter a more advanced type of football.
So it's no coincidence sleight of hand is also part of this multi-back renaissance, too.
Confuse and clobber - Football Study Hall