One simple reason why the twenty first century will not be great for astrophysics. No one will be around in 0 to 50 years.
The ultimate law of the universe, probability balance, is strongly suggesting that humankind's amazing run must be nearing tis end. All good, creative things have a built in destructive offset. Ours is spreading stockpiles of nuclear weapon and global warming. One little technical glitch here or there or some madman goes tilt and it’s all over in a matter of a few minutes.