According to this site , 5.9 million(lets make it round - 6 million) PSP has been sold in Japan. Software, total 11.8 million (round number 12 million).

So attach rate is 2 to 1, meaning every PSP owner has "only" two games. Unfortunately i can't say about situation in US since there are no "total" software numbers, but it most likely isn't that much different.

What could be the reason of such low attach rate? Lack of good game? Hardly! I don't own PSP(yet) but from what i know it is very easy to hack it and play backup/pirate games, that is most likely main reason.

What are your thought on this one?

i don't own a psp but i'll make a guess.
psp is more like a media device than a gaming device.
you can play videos, music, blah blah...
I think people get distracted and don't really look at the gaming part.
The weight and size and the fragile-ness doesn't make it "too" portable.
I personally hadn't seen anyone carry a psp with some sort of enclosure to protect it, in turn increasing its size.
You really have to have a dang big pocket to actually pocket it.

other reason that i usually hear is that psp is basically a handheld ps2. why play on tiny screen when you can enjoy the exact same thing on a big screen?

and if the game is release on both platforms (psp/ps2), how many are going to shelve out the cash to buy the same game twice?

To me, however, would have to be battery life. If I can hack a game and play it on memory stick instead of the umd, I'll play it on memory stick which loads faster and at the same time doesn't drain battery life.

UMD is an example of shoving media format down consumers' throats. (I would love to see a new design that do without the umd)

Attach rate of 2:1 is horrible. People only buy 1 game per year? ouch.

piracy, plus remember it's a great portable media player and many people bought it just for that.

On the other hand, many people who own both a PSP and a PS2 find that they're better off purchasing a PS2 game since there are very few PSP games that are truly different to a PS2 counterpart

I've used mine as a personal MP3 player more than an actual gaming device, but I love having the games available.

They probably just download games to their mem cards, so basically yeh piracy

i have like, 30 games on my DS. thats a good attach rate >:FD

I know , its a bit weird . I was shocked , when I heard in May , that there where less than 17 million PSP software shipments . And you know whats even scaryer ... that from that number nearly 2.5 million are Monster Hunter games . And the scaryest from all : there are around 700 games released in Japan for the PSP , while less than 400 in the US and EU regions ... I wonder why ?
Worldwide , the PSP game software sales are nearly 6-1 , wich is not bad , but it still needs to improove . I hope this year , when big games like CC and Dissidia come out in Japan , that number will grow at least 3-1 .

Edit : I have to over 30 games for my PSP to All original ... but then , If I think a bit batter , Im a freak  

I have around 50 original PS2 games. True, i payed full price for 30 of them, most of the other i bought used or later on when they got cheaper, but still games are original. So those that say that piracy doesn't hurt that much any system are awfully wrong. Attach rate for PS2 is 4.5 i think, overall. Now i am not going to belive that on average people only have some 4-5 games PS2 games when there are SO MANY great games for PS2. Most of PS2 are modded and play piracy games. I am not some hardcore gamer but still i have 50 games. PIRACY hurts a lot, it seems that Sony learned their mistake made on PSP being so easy to mod, so now PS3 is still only "bullet proof" system out there. I am not saying that hackers wont find their way to brake it, but it is going to take time and it ain't gonna be easy now whet it uses blue ray.

I own 4 PS2 games and the 4th was only purchased because it got me a mail-in rebate when I purchased the PS2. It wasn't my primary system and I didn't get it till it was $120. The only reason I finally got one was because I'd had 3 games that I was playing on my brother's system until he bought his house and moved out.