Brilliant Uncirculated coins in the R1 series generally have very low mintages and very few of them get graded - when they do it is usually by serious collectors.  Often, the MS coins command much higher prices than PF versions.  This is because of a two-fold problem of low mintages and few being graded other than by collectors.  Often, proof versions get graded in hopes of selling for a profit by dealers, whereas the uncirculated versions were almost always sent in with the express intentions of adding to a collection.