Jack Ma doing this is also a political move. I'm sure that part of the motivation is just to help, but it seems clear to me that this is also intended to show that China is in a position to help the US, and the optics of that are that the countries are on equal footing. Remember, China as a country does have a bit of a complex about their status, which is completely understandable considering the rapid changes they have been through. This aid shows that, rather than being a 2nd-class citizen, the country is in a position to help America with something.
That being said, this is a great thing, these are much needed supplies for which there isn't a large domestic manufacturing capacity (as it was offshore). However charitable acts can also have additional political motivations, and that does seem to be a factor here.