Bad luck Nicole. Hope she does well in doubles.
Re Trudi, maybe it's a financial thing. As we all know playing on the tour is expensive, so if a player is chasing singles wins, a player ranked as low as 400 is only ever going to make qualifying in much lower ranked tournaments. However, with a healthy doubles ranking, being able to enter higher tier tournaments are possible, and a greater financial reward achieved. As at 15 September Trudi has earnt $40k with 36k coming from doubles. Being high enough ranked to make it into doubles at GS is so important to these lower ranked players.