MS may have chosen to respin the chips to get better yields. They may have spent more money in fixing any issues that cropped up and hoped to recoup it with better yields and higher performance.
The variable route doesn't to me sound like an ideal situation. You can never have more than the max clock speed but can now have less than the max clock speed. Just sounds like a recipe for an uneven experience for some users
except the point was to make all PS5s act the same unless I’m mistaken?