Why would a trail account spend real money to get NIC but not to subscribe his account?

You can do this now with Non-Trial accounts.
I see no reason why trials should be blocked from receiving NIC.

they have all the trials gimped to prevent cheating all tho dont think the dev even know the extent of it

example dev tried to have private convo with me and learned that even a developer cant talk to a trial account unless your in a squad with them.

they are work arounds tho that i found if you want to put nic on a trail account its not hard there is a way  me posting it will prob get it blocked as well.

this has worked for me not saying it works all the time.

log onto your main account buy a field container deploy out of station i didt move at this point but dont think moveing matters as long as your with in range of the term and can enter it. log on trial account and you should be able to access the container with a trial.

now i did testing and out in the field trials cant access a field container but if you are right at the term as in you can click the button to enter then a trial can acces the container.

once you have the container up and your trial can open it simple drop in few thousand reactor plasma grab it with your trial char enter station and sell it.

and you now have money to buy ammo on trial etc not that its good for much else as only npc orders are avaliable but its good way to get started with ammo if want to buy mods i would sugest just buying them on your main account then putting them in the container and tradeing them over. before ya drop the money better make sure it still works been about week since i did it last.

also dont put your trial char in a squad while doing this as it sometimes blocks them from accessing the field container something about when in squad you dont need to enter the password.

That's still not really a reason to stop them from receiving NIC.
Buying NIC will get you banned, and if they do they can't abuse it.