Because Ryan needs love too.
i need to ask u something, why did Ryan need to be replaced? Can't he just be healed and then he can perform again? Or is it like a permanent injury, so if it does heal and he continues to play drums he'll just injure his arms again? and the 2005 tour, when all six of them were together, what did ryan and matt do? did they switch turns playing drums or something? I was about 8 that year, I hadn't developed enough love for maroon5 and had always know them by songs, not them personally. IMPORTANT.

haha this is a great question. I’m going to answer it the best I can, and if someone feels like my answer could be improved/is accurate and good, send me an ask!

The Live Friday the 13th movie kind of sums this up for me, since I was about 12-13 and a huge fan at that point. 

Ryan used to play baseball as a child, and he was a pitcher. Now I don’t know how the guys in the MLB do it, but pitching excessively without PT/rehab in between can be eventually damaging to the shoulders, IF the shoulder muscle is always excessively being used later on in life. Which is what happened to our dear boy. 

Things were fine when their touring schedule wasn’t packed with daily events, but the more popular SAJ got, the more dates were added to their tour. And the physical stress of paying daily took a toll on Ryan’s shoulders, and it became painful for him to play. If he could just be healed and perform again, it would be the best thing ever. But I think he was to the point where the damage was done; I’m not sure if he could have gotten surgery, but that would have kept him longer from touring etc. You can only rehab a long lasting injury to a point where there’s nothing else that can be done, because sometimes surgery is worse.

I’ve devastatingly never seen Ryan perform with the band, especially because Matt plays the drums on the Live DvD. When Ryan wasn’t playing drums, he sung back up vocals from off the stage, which breaks my heart. Matt kind of tagged along, and when Ryan just couldn’t be up to it, he played instead. So essentially, they switched turns. 

I hope I did a good job of answering your question :)