christophkk said:
initiate an exchange yourself. give them some resources or money, if you have a surplus
I've never quite figured out when and why allies make decisions about handing over blueprints, but this is good advice.
Sometimes, it seems clear they don't because their diplomats are too busy making and cancelling trade agreements to alleviate minor perceived shortfalls. For instance (despite having a strategic oil reserve of, like, 80,000 in London) minutes after it occurs, the USA will be offering my 22 units of free oil. And since they're doing that, they're too busy to give me all that cool technology.
One thing I noticed, though, is that trades initiated by you in DD are far more reasonable than they were in HoI2. Then, it seemed you had to offer 3-5 techs *plus* a big pile of resources just to get one of theirs. Now, a one-for-one tech exchange is easy, as is a fairly small pile of resources-for-one tech deal.