Well, It's not impossible just hard and some creators are better at it than others.

That's true. So true.

Kudos.

Another reason may be the fact that a lot of devs take out features from part one but add new ones to part 2.

For example:In Star Wars Battlefront you could go prone on your belly. BF 2 had playable heroes and no Prone. Smackdown vs Raw games always take out good features and add good features each year.

I know those games arent considered classic, but a lot of games now a days do that. Take out something good, add something good.

Or it could be that game developers lack the capacity to meet or exceed the expectations set by the previous game.
Like Sega did with Sonic 2 or Capcom did with Mega Man 2.

One time my copy of Pokemon started cooking breakfast so I had to call the cops.

so that's why deca sports 2 sold less copies that deca sporta... I was looking for an answer to this mistery, thanks for the information

This is exactly the reason why you are seeing more sequels to crappy games. It's easy to improve on them.

Sometimes sequel tries too much to change something that is not broken.
Sometimes they forgot fans and try make new fans.

Or simply, first game is best there is (Dmc,Mgs,Grandia,Dino Crisis,Onimusha).

That is, unless a sequel manages to become much better than the original, games like HL2 which is considered better than HL1, WC3 better than 2, MGS4 the best in the series (and ever too!).

Now, Uncharted 2 seems to be able to do just that, it adds a lot of features that the first lacked, and improves on any front, most important of which (for me at least) is going from mainly arena battles with waves of enemies to the way it is now, for which I don't know the words in english

or, you can just make a game exactly like the one before it, like in the case of mario 14, zelda 8, halo 5, or MGS 9, ff 32