Is there ever a reason to not get these boots. 40% cc reduction and some MR. I feel that all the other boots don't even compare to what they give.

The other team has no hard CC.

When you aren't gettin stunned too much cuz you're a boss kiter. When you have awesome MS modifiers that make it pointless to even stun you cuz you're so fast.

or when the opponents stack knockup, The Better Stun (TM)

if you are playing a mage/they have no cc only time i dont get mercs

I feel ripped off when i buy those boots(which is pretty much every game) because the tootltip says they also reduce sleeps by 35% but there are no sleeps XD

Some champions, when they get CCed die instantly anyway. Therefore it's better to get other shoes that make you do as much damage as possible before that happens.

If you have Cleanse or if you're playing a champion that will die to CC regardless of Merc Treads.

When the other team has...Katarina, Corki, Ezreal, Mordekaiser, and Soraka.