"The Defense Department has said that strategic competition with China is the U.S.’s primary national-security imperative, including deterring conflicts in the Taiwan Straits, the South China Sea and other areas of the Indo-Pacific region. That requires a bomber that can evade enemy radar through a stealth design, achieve a high top speed and carry a payload of advanced weaponry that it can drop it on many targets in a single run, defense analysts say."

That might deter something if it was plausible that the US would declare war with China by using the B-21 to bomb Chinese targets. However it is highly unlikely that the US would do that unless attacked first, which China is equally unlikely to do.

This program rather sounds like an expensive way to keep the industry afloat and the know-how at the cutting edge.

If the B-21 sees action the most probable is to carry out air strikes on groups like ISIS or the Talibans (which, apart from Kosovo/Serbia, is what the B-2 has been used), and just because they will be available so might as well be used.