The lack of Crossrail station at City airport (LCY) seems odd at first glance, but when you look harder you can ask - would it really be worth the cost? City airport already has the highest public transport usage of any London area airport - more than two thirds of airport users use public transport. The DLR might still have a "mickey mouse" reputation with a few folk but the frequent flyers who use LCY (in general - travellers who value time and convenience over cost) have long ago realised that the DLR and Jubilee link is the fastest / quickest / easiest way into central London.
As for passengers at Woolwich wanting to get to London Bridge, well - errr - they already have direct trains. (On the occasions that SouthEastern can be bothered to run them....)