Malzahar's ult can't be cleansed?

I just played in an ARAM as Tryndamere , and I brought cleanse due to the typically heavy possibility of many CC heavy champs being on the enemy team, and one of the enemies was a Malzahar .

Now, if you read the description for the summoner spell "Cleanse", it reads like this: "Removes all disables and summoner spell debuffs affecting your champion and lowers the duration of incoming disables by 65% for 3 seconds." I found, however, that Malzahar's ult couldn't be cleansed, regardless of how many times I try to spam the spell during it. Luckily, though, I was playing Trynd, so if he got me too low, I could still ult and not die, but this OP inability to be cleansed is still a rather large inconvenience. What's, if I may ask, is the point of having a spell that's ability is supposed to be "remove all disables" if it cannot, in fact, remove ALL disables? If it's able to removes stuns, why is it not able to remove suppresses?