Why Does Mundo Ult Have a Cost?

Because then he'd really have no choice on whether it's worth it to ult or not.

its to encourage him to use his ult at a lower percentage

Mundos all about managing your health, so watching how quickly you take damage in teamfights helps you determine the last possible second you can ult without dying. That's what I am making up anyways.

Your argument is stupid, but I do think Riot should look at the health cost vs. gain of Mundo's ultimate. His effectiveness drops by a truly absurd amount if the enemy buys grievous wounds to the point where it feels like he wins games if they forget to buy it, but loses if they remember. The cost on his ultimate is felt much harder when they buy grievous wounds because the healing afterwards is supposed to make the cost feel paltry, but that healing gets dramatically reduced.

Asking a question is not worth all the downvotes you're receiving...

That being said, it's important that Mundo's R has a cost, even if it breaks a pattern. It makes it a more interesting and interactive decision of when you want to use it exactly. Yes Morello is annoying and push you in the other direction, but that's another issue.

Mundo's ult should have a cost, it rewards casting in anticipation of taking damage.

Mundo has other issues. Riot seem to think (or did) he is a lategame champ but the only items he is strong with lose their value late. Mundo is extremely weak, riot take 75 hp off loads of tank items, gut sunfire, and then add 5 magic damage a second to his w. I remember when I started playing this game and got into Mundo my opponents were focusing me then getting killled by my team even if they killed me. Bronze players and pre 30 dont know how to play vs mundo and he looks easier to kill than he is so he gets gutted.

Everyone is crying about Garen but he is stronger than Mundo.

http://i1146.photobucket.com/albums/o532/blazeandraze/mundo%20lategame%202_zpsamuf9am6.png