Because as authors we try to go for believability and if we attempt to make Michael an integral, biological part of the Evans family, it wouldn't make sense to have his last name as Guerin. It's not like we changed his name to NevilleSundae wrote:You know what really annoys me...and this is in regards to fan fiction.
Its when writers make Michael either a Evans or a Valenti. I'm sorry but I don't want to read about Michael Evans, nor do I want to read about Michael Valenti. I want to read about MICHAEL GUERIN. Yeah yeah, I know that it helps streamline your plot or makes it easier for you to make Michael someones brother...but it bugs me. It never use to, but for some reason now it does. I feel like it takes something away from the original characters and face it, I'm in love with the original characters more than I will be with another other made up version (no matter how good the writing). The last name holds a lot of weight and I don't see any reason why you can't make Max and Michael brothers with different last name...would it be so hard to quickly state a reason for it and then move on with the fic accordingly?

You should still be able to visualise him and (if the author's done a good job) still see most of the same character traits, whether as an Evans or a Guerin or another last name. To me, his last name really isn't important at all. Keep the first name, but Guerin doesn't really add anything to a story and would only create a mess that the author would have to clean up. Plus if they only add in a sentence about why his name is Guerin it would really mess up the flow of their fic and it would look like an add in just so that they could keep the Guerin last name in there. To me it'd look a bit messy and totally unnecessary.
But that's just my opinion. I've never had any issue with any characters having a different last name so long as I could still recognise their characters. I'd rather see a well developed Michael Evans than a completely out of character Michael Guerin.