Sorry if this is a dumb question. Couldn't find any previous posts that asked this question: Why are all completes that have less than a 20.5" top tube made of hi-tensile steel? I've never seen a 20" TT frame complete made with chromo let alone full chromo. They always seem to be made of hi-ten. Is it because smaller and therefore younger riders who can't afford full chromo tend to gravitate toward the cheaper hi-ten completes? Or is it some engineering reason? I doubt the latter because I've seen 20" frames that are full chromo, just never on a complete bike.

You have already answered your own question.