HS Precision uses graphite/kevlar stocks on the M24 SWS and they survive the demands of US Army snipers (dropped, slammed, you name it it happens to the stocks)
McMillian stocks are fiberglass and the Marines use them on thier sniper rifles, in 30 years use only 2 McMillian M40A1 HTG stocks were sent back to McMillian because of cracks in them
wood stocks wouldnt hold up nearly as well they would be effected by the elements greatly, warp, shift points of impact in the heat if not glass bedded etc
and they would crack easier than a quality plastic stock
but there ARE cheap plastic stocks that SUCK and i could crack them accidently but rest assured that kind of plastic is only on poor man's hunting rifles, NOT world class sniper rifles