Because the Yankees play in the majors.

Inbox with Felz:

"Why did the Yankees decide to sign Youkilis as opposed to giving the position to a Minor Leaguer until Alex Rodriguez is ready? They'd save quite a bit of cash and might discover a future star or trade bait at the same time.
-- Al S., Morocco"

The Yankees should play a theoretical minor league third baseman for half the season so they can either save quite a bit of cash (and spend it on a player like Youkilis) or so the minor leaguer will play well and acquire trade value (maybe for a player like Youkilis).

Or the Yankees can just sign Youkilis.

Thanks for writing,
Felz, America