likely the same answer as to why the SR-71 is discontinued - advances in satellite reconnaissance and UAV technology made it irrelevant.
What advantage exactly does a B-1B have over a cruise missile? What advantage does it have over some UAVs sent on an autonomous mission? Bearing in mind that you can easily fire off a couple dozen cruise missiles just for the airframe cost of a B-1 let alone the training, etc.
A manned pilot is some better in some respects, but is it enough better to justify the additional cost, training, and the downsides that come along with a manned mission (political risk, etc)?
For certain missions, the B-2 and the B-52 etc have their merits, and close-air-support with a UAV in non-permissive airspace seems like a bad idea. But by and large the trend has been and continues to be using unmanned and expendable platforms to replace a lot of roles. The B-1 doesn't do anything that a cruise missile really cannot replace.
I'm not so sure. Airplanes are hard to keep secret when they're flying around, and existing planes have their capabilities pretty well figured out by now. It's not every day a new airframe is built.
I'd expect the $100MM USD F-35 to have all the latest tech, being the newest fighter available.
