It wasn't the way it was supposed to be, but it was the way it was. I can't point to lots of specific episodes, but I'm sure the Doctor told his companions several times that they couldn't change things because they had already happened, not just fixed points, but pretty much everything they had experienced.Why? Why should the Doctor have simply accepted it at that point? He's the experienced time traveler, and he knew that wasn't the way it was supposed to be.
He could have spared Jackie a year of worrying about her daughter and thinking she was dead and he could have prevented Mickey from being a murder suspect, but he didn't say "Whoops, back into a TARDIS Rose, next stop last year", the characters had to deal with it, because that's what it was now.
Of course that was before the whole "Time can be rewritten" stuff started, which I really don't like that much.