Maybe some got interested in the franchise because of the second son hype so that some bought the first game to start with the franchise and to check if they like it or not.

Infamous was free for everyone after the PSN hack.

Just looking through some other games now.

LBP
2013: 290k
2014: 40k

LBP2
2013: 295k
2014: 32k

There was 3 years between these releases. I wouldn't have thought there would be much difference in retail price, all this games would be in the bargain bins by this stage. Is it just new adopters going for the original titles?

I think it is simply because people who learn about inFAMOUS was to start with the first game, and those that try the first game in many cases don't graduate to the 2nd game.

I think inFAMOUS 2 is much better than inFAMOUS

I think inFAMOUS Second Son is just phenomenally good on gameplay, while the prior games were better on story/character depth.

This.

The first Infamous was okay, but I thought it received some pretty overrated scores.  Cole was so slow, his skillset was fairly limited throughout the game.  the enemies regardless which area you were in were the  same enemies, and the city in all three districts were mostly the same. 

In Infamous 2 however, first thing you'll notice is how much quicker Cole is than on the first game.  That alone really makes all the difference, even if you couldn't use a large array of new powers, the movement and how they sped up traversal made it more enjoyable to play.  I wouldn't have thouught it would have made the game more enjoyable though if I didn't play it myself.  Cole in Infamous 2 got a large variety of powers so if you didn't like one skill, you could always switch it to another  that you did like to use.  There are a lot more different enemy types than just random enemies with guns or the lightning, summoner, and large guy with gun conduits you rarely ever fought.  The only difference in the enemies in the first game was that they got more HP.  Infamous 2 actually had multiple different enemy types and several different enemies of those types.  The enemies with guns make a return, but then there are the monsters, and the ice enemies and each one had several different versions.  Depending on your location, the city in each of the three areas were vastly different, but within each of those areas, there are a lot of unique areas as well.  The second area in the game is both flood town and the train yard for example, and the first area and third area had several parts that were very different from other areas.  Also the second game also had better missions, better side missions, etc.  Overall a much better game overall.

The only thing I think the first game had over the second was the story.  The story in the first one was better, and that was only because of the ending.  If you played the second one first, the ending may not have been that good.

no, 2 was better in everything but the story, which imo was better in the first one

that said I believe the games are just too similar

I don't think vgchartz game sale stats are reliable. Are they ?

Infamous > infamous 2

It's simple really. You start with the first game if you want to start a series. The sales missing for Infamous 2 are the ones that weren't impressed with the first.