The imperfections is one reason, but also, briar is the from the heart of the heath tree where the trunk and roots come together. This is not a large tree like a cedar or elm, but rather a good size bush. As such this heart is rarely over about 5-6 inches across. This means that to find a briar with a good enough length of wood to make a scale without imperfections, you need to get an uncut block. The cost to take a good block like that away from the artisan pipe makers is going to be pretty high, but I admit, decent briar scales on a vintage blade would look pretty darn cool.
Gillette has a cartridge that went 5 weeks? My straight has gone 5 generations!