Loads of people can correct their vison to the reqd. standard, however, there is no guarantee that their corrected (with spectacles or surgery) will stay within limits.
There's no certainty that a person who makes it without correction will always stay in limits either, but they are far more likely to either change very slowly, or not at all.
I passed the UK mil reqs in 1977, and I'd still pass them today, though with spectacles I can see far away objects slightly better.
Why waste $millions on a high risk candidate, when in most countries, you have plenty of lower risk candidates.