Why do people say the TV show isn't canon?

I really liked the TV show so much that I've seen it twice so far but I've seen some people saying that the TV show isn't canon, has major plotholes/isn't consistent with previous game lore, and that it somehow makes New Vegas not canon anymore.

Now I haven't played all of New Vegas yet, but I can't think of why Bethesda would allow the show to retcon one of their most popular Fallout games or how it even would do so.

I also haven't noticed any major plotholes, sure there's Shady Sands now has skyscrapers when in FO1 it was just simple concrete looking shacks but I think that could be explained away with artistic liberties which also could go for the walk to Shady Sands taking less time than it realistically should have, it just wouldn't make sense to spend a whole episode on them walking.

Are there any genuine flaws in the plot that isn't consistent with previous game lore or are people just hating because it's a videogame adaptation?