Zhonya's Hourglass and full ult cool down

I was playing a game of aram as Veigar and the game was going fine. As the game progressed every time i ult the enemy Swain he would hourglass and that's fine but what was annoying me was that my ult would have a full cooldown. It seems really annoying that even with veigar ult which is pretty instant that hourglass can just cancel it and i have to deal with the full cool down. I'm more looking for an explanation of why this is the way it is. Maybe instead of a full cool down maybe get 25% refunded so that even though you didn't get the ult damage you will have your ult back sooner as compensation.