The reason is ceramic mags are very brittle therefor difficult at best to make rod stock with.
Strat mix ceramic bar alnico.
They are not themselves permanent magnets.
Single coils can use alnico poles but like the barden there is no room inside for a ceramic so it gets slung below and connects to paramagnetic poles i e.
To my ear much of the personality of the strat is lost with this type of pickup.
Wilkinson low gauss vintage tone ceramic st strat single coil pickup for stratocaster guitar middle white.
Alnicos would be stronger but the main difference in sound characteristic is more the shape and subsequent coil engagement than the substance the magnet is made out of.
Bangdan alnico 2 bar magnet 2 5 x 5 x 125 for humbucker and p90 pickups 2 pcs magnetized.
With windings like for like the ceramic will usually have a thicker less stratty sound with a chunkier midrange and less definition.
Bar mags for ceramics are black.
4 personally i prefer the alnico single coils for the reasons i listed in 1.
Alnico vs ceramic magnets.
Strats are always alnico poles unless there is a mag attached to the bottom then the poles are generally 1018 or 1022 slugs.
Humbuckers come with alnico or ceramic magnets and people mix them all the time.
Fwiw the barden tele neck pickup is my favorite tele neck position pickup and i ve tried a lot of different tele strat mini humbucker full size humbucker ceramic alnico pickups ymmv of course.
Alnico seems to be the popular favorite but on the other hand there is no shortage of popular recordings that feature ceramic pickups.
My opinion there would not be much difference if we could test ceramic poles versus alnico poles or ceramic bar versus same size ceramic bar generating the same field pattern.
Get it as soon as thu oct 8.
The ceramic pickup non magnetic poles plus bar magnet has a different tone from the classic alnico.
The bar magnet on a humbucker or mini whether alnico or ceramic is tucked away inside.
To crown a winner in our alnico vs ceramic magnets shootout we would need a way to accurately compare the two which is not an easy task.