Would they be available after reaching lvl3?
Whether they are available at level 3 or before (which I don't know), I don't think that's the only reason, since for other rewards they say we have to get lvl 3.
In other words, there must be another reason, hiding the "you must be level 3" message if that's a requirement.
Well, i think CSGO skins are in demand,
So due this they are unavailable for most of the time
Think they put it a lvl 3 is to prevent people from creating throwaways to redo the same XP churning spam and to allow acutal people to get the rewards