Complex sentence: In the USA, where this position was until recently relatively uncommon, it has enjoyed a recent growth, particularly in theater companies that focus on developing new plays and those that produce plays where the socio-historical background is important to the understanding of the production.
Split into simpler sentences: In the USA, where this position was until recently relatively uncommon, it has enjoyed a recent growth in number. The dramaturg position typically is part of theater companies that focus on developing new plays, as well as those that produce plays where the socio-historical background is important to the understanding of the production.