Friction shifting it is You that moves the chain from 1 cog to the other ..

because 10 has to fit in the space of 8, the gear shifting you do with your hand requires more Precise feel.

lots confuse the trendy sales websites for the repair parts sources Bike shops Use ,
and with so many 9 speed bikes on the roads ... believe Me ...

You can find parts .. in regular shops that repair existing bikes.

& 8 speed stuff is still being put on New Bikes,

and 5,6&7 speed freewheels are still made.