My first guess is availability. 2.5's were only found in 98-01. OH....for what it's worth...the 01+ 2.3 Duratechs are totally different than the 2.3/2.5 Lima engines.
I don't know much on the subject, I'm just learning. I intend someday to build my own 2.3T and in the very least, help by brother build his. The guys over at TRF are a pretty cool group of guys always willing to help new guys just starting to learn.
'01 XLT disguised as a '03 Fx4 Level II.