what would have been the difference between 3♦ and 3NT as your choice for a first call. IMO partner would think 3♦ is for a major preference initially and maybe for ♣/♥ after 3NT. Whereas a direct 3NT would have had to take into account a possible weak reopening X and should show 2 or 3 ♠ partner is now better placed to evaluate how to proceed