For one thing, a GUI client needs a GUI, which is a massive amount of overhead for machines that have no screen, no mouse, and no keyboard...
And for the other thing? *fg*
Hmm .. you mean this GUI-overhead results in about, I guess, ~ 20% of useless allocated RAM, of the total bitcoin-qt client? *LOL*
What a huge waste of resources. :->>
I believe it was a historical design decision for "prettyness", because the old GUI (wtx) was simple relative independently coded from the remaining code - or the new GUI (qt) was independently coded such that it was easy to get a GUI-less client, too (in the case that in the future the GUI will be changed again to a different library/API) -- well, my speculations.
smtp