OK, there are a few things that need to be pointed out.
1. Score inflation: you can blame this on reviewers praising everything too much. When lots of games get high scores, those scores mean less because getting those scores no longer means that a game is better than most other games. Technically, 5/10 is supposed to be average, but it ceased to actually mean average a long time ago and only a few games get that score; no-one complains about 5/10 being considered bad. Maybe the same thing is happening with 7/10, which has been "average" for as long as I've been reading video game reviews? Maybe score inflation has reached such a level that 8/10 is now average?
2. For games that are hyped, average is bad, so 7/10 is bad even if it is still average. Hyped games are supposed to be very good, so when they're not, it's a disappointment. For any new numbered FF game, for example, 7/10 is awful. It's like an A student getting a C. For some students, a C would be fine, but when a student who usually gets As gets a C, something has clearly gone wrong.
3. Average isn't really worth spending money or time on, unless you have lots of both. I can't afford to spend all of my time and money buying and playing huge numbers of video games, so I have to pick out the ones that look like they'll be the best. If there are several games with 8, 9 or 10/10 in the genre, a game that gets rated as 7/10 by most critics will be at a severe disadvantage.
4. Well, average is just, bad, y'know? As someone said earlier, people want to play good games. People want to play great games. Few people want to play average games, unless they are huge fans of the genre and the genre doesn't have many good games that they haven't played yet. If "bad" means worse than most games, then average is not bad, but if "bad" means "do not want", then anything that is not good is bad, therefore average is bad. Actually, this relates to Sturgeon's law.If we accept that 90% of everything is crap (and I believe this to be the case), then average things are crap.
