Serious question, Why do they have two pairs of goggles?
The over helmet ones are standard issue across the PLA.
They would create an air tight seal around the eyes when worn properly and would be very useful in dust storms and keeping out smoke and gas etc. Obvious they won’t be up to NBC standards, but should suffice unless you plan to spend prolong periods of time in smoke/gas filled environments.
The problem is that they become uncomfortable to wear very quickly due to the same air tight seal. Coating should mitigate fogging, but it’s going to be unpleasant in all but winter conditions to wear them for any meaningful length of time, which is probably why you hardly every see PLA troopers actually wear them.
The ballistic glasses are probably reserved for special forces for the most part in terms of standard issue, but are light and comfortable to wear basically all day and all night long should the need arise.
If I’m honest, there is probably also an element of anti-theft in not using ballistic glasses en mass. No one would want to steal the over helmet goggles, but ballistic glasses will probably go missing on an industrial scale if it came standard issue in peacetime. There is just no need for it.
The PLA would have vast inventories of them for actual war time deployments, and Chinese factories can probably churn out enough to give every man woman and child in China a pair within a ridiculous should period of time during wartime economy conditions.