I have heard of 'second market', but how would one go about doing this? Do they create private contracts and such for a non-yet-listed company?
The company can do this for the same reason they can force employees to wait six months after IPO to sell their shares, it’s in the contract you sign when exercising your options.
Which is why selling options is a loophole…
Worst case you can always exercise whatever portion of your options you can afford and accept the inherent risks for doing so.