I had done tons of RTW flights prior to Covid, and as other posters have explained, the fares can fluctuate based on the booking codes of the issuing airlines.
As other have suggested, find a competent travel agencies that have experience with RTW in all the major alliances. They often will come up with suggestions that can save a lot $.
My RTW days are over due to career change, but I will forever miss the ability to fly RTW in business to add a few excursion stops between businesses destinations.