Who knows how the epidemic will develop.
The underlying issue is that these blocks come out of the blue, with no warning.
As well, restricting visitors when they declare they've been to Hubei is not likely to work. Folks don't want to end up turned back or in quarantine. So they don't declare their Hubei visit. That may force HK authorities to take far more comprehensive measures.
There are mounting calls to close the border with China entirely. That would be drastic.