It’s to do with the loading mechanism, usually.
Solid-Frame revolvers (such as the Colt Single Action Army and the Nagant M1895) rotate clockwise, because they load from a gate at the rear of the revolver and it’s easier for the firer to index (manually rotate) the chambers clockwise to eject the shells and load new cartridges.
The Webley top-break revolvers rotate clockwise, as do most other British revolvers. Ruger GP-100, Security Six, and Redhawk revolvers rotate anti-clockwise, as do (I believe) Colt Police Positive and S&W Model 10 revolvers, but it’s been a while since I’ve had a chance to play with either of those.
FWIW, It’s been my experience that swing-out cylinder revolvers generally rotate anti-clockwise, whilst solid-frame and break-top revolvers rotate clockwise.
It’s easier to get the cylinder on a swing-out revolver to “roll” out of the gun if it rotates anti-clockwise (towards the left, the same side the cylinder swings out), whereas on a solid-frame revolver it’s easier if the cylinder rotates clockwise to facilitate ejection and loading, whereas in a break-top revolver it doesn’t really matter which way the cylinder rotates, since the revolver breaks open to reload anyway, so I guess they went with “Clockwise” because that’s how most revolvers rotated at the point the top-break design became popular.