I started a thread on this a few weeks ago saying the same thing --- so needless to say, I also agree with you, and it's a complaint that I've had about every Civ iteration since Civ I. They finally did it in SMAC, which I loved, but then reverted back. But it appears that folks like us are in a tiny minority and people just don't care about it.
I can see the argument for having the same text for each leader --- eventually you no longer linger on the diplo screens and you want to move through the game as quickly as possible --- thus, having different text for each leader forces you to read it only to discover that it has the same effect as different text for another leader. I can also see how unique flavor text can be distracting --- so in SMAC, if you were Miriam and you were condemned for pounding your precious bible, you never actually did anything that involving bible-pounding so it was arguably weird.
However, the easy workaround to this is to simply have a parenthetical at the end of the text (they do this in Civ 5 already) explaining the practical consequences of what is happening (e.g., they are condemning you, or whatever).
Another compromise I hope they already did, is to at least have different flavor text for different AFFINITIES, as that would actually communicate something about the ideology that they've adopted and care about.