Perhaps you haven't really answered the question? The questioner asked why the feast of the Assumption is not transferred to a Sunday.
The answer is that feasts of the Lord are transferred, but not feasts of our Lady or of other saints. The explanation is that Sunday is already a feast of the Lord, "the foremost holy day of obligation in the universal Church", as canon 1246 puts it. Transferring a solemnity of the Lord to that day is consistent with the honour given to the Lord every Sunday. Feasts of our Lady, or of other saints, are a different matter; all else being equal, they are best suited to celebration on another day of the week.
Does that sound right?
Commenting by HaloScan
