Playing conditions have improved greatly since 1966, when there were a lot of grass fields that wore thin late in the season and no domed stadiums (the AFL’s Houston Oilers didn’t move into the Astrodome until 1968). What first-generation artificial turf fields existed tended to be more like hard doormats than natural grass fields.
Today, seven teams play either in permanently domed stadiums (New Orleans, Detroit, Minnesota, and St. Louis) or in retractable domes (Houston, Phoenix, and Indianapolis).
Great improvements have been made in the look and feel of artificial grass fields to the point where sometimes it’s hard for TV viewers to tell the difference between the real and manufactured fields. Even teams that elect to play on grass have gone to sophisticated growing and drainage systems that help the fields hold up much better than in the past.