Mmm no, that’s getting history and the causal relationships a bit backward. The early guitars, like their predecessors (lutes), all had moveable frets, and their designers were trying to figure out how to fret various other tuning systems before 12-TET became the standard:

https://scholarworks.iu.edu/iuswrrest/api/core/bitstreams/5c...

Some lute players were arguing in favor of equal temperament, and others were arguing against. It took a long time, but equal temperament eventually won, and the guitar we have today is the result of European music settling on equal temperament in general, not just for lutes, but for keyboards and ensembles. The guitar is fixed and fretted for 12-TET for the same reason the piano is tuned for 12-TET, because that’s the best compromise for all musicians. Guitar wasn’t designed to add warble, it evolved along with other instruments to support enharmonic modulation, which requires allowing a little warble. If we could have guitars without the warble, we would.