That's exactly the point. The tax breaks were allegedly going to stimulate the economy for the average worker (you know the forgotten man Trump loves to talk about). They weren't supposed to be hoarded by the corporations for bigger profits and share prices.
Providing a tax break just to increase corporate profits is inefficient because you're much less likely to see that money returned into the US economy. Mailing checks to people would be an inefficient economic stimulus as well, but at least when you do that you know the money will end up back in the domestic economy. If you give it to a big corporation, it could end up as an investment in the Chinese economy, and the government will still be subsidizing the big corporation's underpaid workers with federal assistance programs. In that case, you lost a bunch of tax dollars to line rich people's bank accounts.