I can get away with 700x25 or 700x28 tires on a steel road frame.

If I try that on a Cannondale (I have one), it tries to shove the
seat up my ass.

As others have stated, there are significant design differences
in the tubing and the frame use of it between the two materials
that attempt to use the different Young's moduli to best advantage.

Also, aluminum makes much better beer cans, hence the term
"beer can bikes" you see often used on the C+V.