It's all about raising barriers to keep foreign business out in the guise of national security.
And specifically it's about shielding the domestic telecom monopoly system. Verizon and AT&T wave their magic wand and Congressmen dance. A Chinese carrier would very likely come in and compete on price. Softbank is likely going to do just that as well, and I'm sure the last thing VZ and AT&T want is another competitor on price.