This may be a silly question: I just looked at the Cat Bordhi video on youtube for knitting moebius scarfs and although I can most likely do the technique, why won’t just twisting the stitches on a circular needle work as well?

Because just twisting the sts puts a full twist into it and still results in 2 actual edges - the CO and BO edge. The mobius CO makes a half twist and your knitting grows from the middle out and has only one edge. The CO is like the provsional CO shown here, except you use part of the cord instead of scrap yarn.