A lot of countries went to bakelite parts early on. Some used laminated wood and others used hardwood, but the synthetics seem most common.
Another issue is that the grip is potentially a 922r compliance part, if there aren't enough other US parts to keep the count up, putting a foreign grip on there could be a violation.
Ironwood makes some wood grips for AKs along with other wood furniture. Since it is US made, it keeps the parts count up as well.