There are 2 major reasons why OneUI 7 is being delayed. 1) S24 -> S25 is not a major jump hardware-wise. If S24 series gets properly optimized OneUI 7, then it'll start functioning more or less like S25 series. This would result in people leaning towards buying S24 series over S25 series.
2) OneUI 7 is actually a major OS Upgrade in the history of OneUI. After OneUI 1, OneUI 7 is the major overhaul be it in terms of functionality, or smoothness or fluidity. So optimizing it properly must be requiring intensive testing. But this still doesn't explain this much delay though.
