There is alot of woodworkers, simple possible reasons is that it's fairly cheap to lvl up to 69, 60% of your synths will actually draw you in a profit.
Another good reason is woodworking is a craft that can make you money, everyone will always need to buy arrows and ninja tools(especially shihei). I highly recommend the craft if you were to start a craft. There's about 5 guides out and the best one I have seen is the one by Cubswoo.
Currently my woodworking is at 93.1+2, I'll gladly make anything for anyone if you bring materials. I also have about 20+ stacks of Kabura arrows, will sell those bastards for 15k/stack.