coach mcd claps constantly and it creates microtrauma that leads to injuries.
ok, seriously this is mostly bad luck. It is true tho, that smaller more quick twitch and faster players are more prone to losing time to injury. part of it is the size they have vs the force they generate/take from contact w bigger players. a sort of under stated part of it tho is a bigger stronger guy can be more effective w some injuries than a smaller faster guy, not to mention position by position.
so, an OL can have a back that needs heavy surgery (spencer brown the other year) play on it all year, and still be a solid contributor. big part of that is brown is a titan of a man, he's 320 lean strong and 6'8 no matter how is back is feeling. he doesn't sprint and change direction and catch balls, or cover guys, so him being a bit more sluggish won't hurt him as much.
a bigger linebacker than milano is less likely to get muscle injuries simply because in order to have the physical impact that milano does he needs to have bigger stronger muscles relative to his frame and size than a larger edumds type backer (who missed very little time in spite of playing nearly all snaps). now the upside is, when a player like milano can hit and tackle like a bigger guy, he's a human missile and wrecks shop when healthy.
another example to sort of support my point is josh allen. messed up his UCL, all but just broke his left hand, but since he's such a savage truck of a human he can still go out there and ball out. chad pennington of much slighter stature would just not be able to go with injuries like that.
so anyhow, size and such does play a part, and we have a smaller d, but luck is a giant part of it, and every team gets guys hurt.