I'll jump on the bandwagon and agree with the previous posters. However, I will not agree entirely. I don't think it can be easily boiled down to "Everyone is afraid of change". I think there's more to it. Everyone sure wasn't afreaid of change before, were they? Obviously not, since the franchises must have started off somewhere. Same with gaming.
When the gaming started to become more "serious", and a lot of new games were introduced, there was a bunch of people who jumped right on it. They took gaming to their hearts, and have enjoyed it ever since. These people obviously weren't afraid of change. I have several different reasons as to why new titles are not as well recieved now as they would before.
I'll even go ahead and share them with you guys. Because that's just how kind I am.
First of. Let me describe a sceonario for you. A sceonario wich will make it easier to understand what I'm about to say. Let's say the local candyshop has two boxes. One yellow one black. You have several good experiences with the yellow one, as that one contains chocolate. Choloate is good. You like chocolate. Now, as the shop-owner is not a kid, or have any relations with kids himself (apart from selling candy to kids, of course) you're not sure if he knows what is good.
You can try and go for the black box this time, but mathematically it's like buying something you don't like. As you don't know what is in the black box, you have no idea if it'll be something you like. The yellow one, however is almost guaranteed to be chocolate. So why would you buy the black one, when you're that sure it's the yellow one you'll enjoy.
They're not afraid of changes. They're just afraid of risk. They don't want to end up with a bad desition. And to avoid that, they go with the familiar
Now it's the other reason. People are dumb. They want a game they can manage to get through. They want "challenges", but not a challenge that is difficult. Sam & Max is a good example of that. The first one was very good, but didn't sell to new heights. So they dumbed it down. They made it easier. You see the mistake a lot of new titles make is trying to make an interesting game. They're trying to give you a challenge. Wich obviously ends in epic fail. Sorry, I had to
When these new titles make games interesting, and challenging people notice that. And the dumb people despise it. Hence drawing a line between too difficult and new titles. You'd be amazed how much damage a dumb person could make. If this dumb person takes a walk to his friends and tell them how bad this game is, they'll believe him. And then the evil circle is on. And reasonable people starts believing them too. Hence making it a lot less lucriative to make new titles.
And if you say that it doesn't matter, because real gamers'll buy them you're right. Almost. It does matter. This might not be known to you, but dumb people outnumber the rest of us. Hopefully they're not going to try and claim the world. They allready claim the right to decide what games should be made, and what should not. It's basicly the same thing with casual gamers. Like Wii is a lot more a console for casual gamers rather than hardcore ones, the dumb games are for dumb people. Casual gamers buy enough Wii-stuff for it to outsell the good stuff. Hence making it less desirable to make the good games.
My third and last reason before I let you go, is advertising. Advertising has a lot to say. A whole lot. The more you get a game shoved down your throat (To some extent, that is. If you overdo it, people'll get sick of it. A thin line, you don't want to cross), the more you'll want to buy it. When you go to the store, and see two different games - One who's been advertise thorughly, and one you've barely heard of - you usually go for the advertised one. Because you'll have more guarantee that you'll like that one better, as you can judge it from the trailers, and advertisement aong with the back of the box. While the one you've never heard of, you only have the back of the box.
And the thing with that is new titles usually don't have the money to advertise as much. Just look at L4D. That was advertised to insane amounts. And it took off into the skies! Other games that I'm sure is at least as good, has never really recieved any glory. Why? Becasue they didn't edvertise. Simple as Dell
Now that's that! I'm off to bed now