Cause IC doesn’t have near the concentrated volume of people that cyrodil does. If IC had the same number of people concentrated in one area as say a BRK or ash siege during prime time it would have the same problems. IC does a better job of spreading people out. Some people at center, some at top, some near based. The lag is because the server can’t handle all the calculations of combat in a concentrated area. Zos screwed up when they designed their mega server technology and now they can’t fix it. It didn’t help they continue to push the servers beyond their limits with adding things like proc sets, new skills, etc.