It's definitely not super weird, in fact on the flip side it's a big reason why so many fans don't read fanfic at all, because they feel anything non-canonical doesn't matter so why waste time with it?

My problem with tie-ins is that they're often just so dull and sometimes aren't any more in character than many fanfics. Some of that dullness probably comes from the prescriptiveness of the tie-in model, but I think another part is simply the author's unwillingness to take charge of the characters which is something that fanfic excels at but may also turn off a lot of people.