But yet some newbies might not want to run old raids.

I mean if you're a newbie, the MSQ will already take you 100-200 hours of play, at least. But not only that, but you also want to dump the old raids on them too and make them required as well, to add another who knows how many hours onto that?

The newbies want to get to Max Level and participate in all this new content that's out, they don't want to be forced to slough through old stuff. Now, some newbies may CHOOSE to go through old raids out of curiosity of the sights and sounds, but I doubt very many of them want to have to grind that stuff for gear.