This is partially because of:
1.Members/Players - I think Microsoft sells consoles now because most people have a 360. What I mean by that is that some (if not most people) buy a console to play with friends. All of my friends have an Xbox but no one has a PS3. Part of the problem is that the average consumer does not know the power and the potential of the PS3 and really don't care. The 360 gets the job done and that is all that the people want. The other thing is that people think that the 3rd party gaming experience is better on the 360 which is untrue to a point; the only reason it can be better on the 360 is that it can be buggy online. (See point 4 for more details.)
2: Past Impressions - When I ask people why do they don't have a PS3, they they don't like it because they feel that it has no games which is not true.
3: A price drop - In this falling economy, some people can't pay upwards of $400. Sony needs to open their eyes and drop the price of the PS3. People can argue that the 360 costs more with the addition $50 Live online service every year. You can also say that Sony will lose lots of money but, they could either be willing to sacrifice money or make cuts on the console.
4. Why not?- I was thinking, "Why does not Sony make a console tier system similar to the 360?". since Sony is going for an entertainment console, they could sell a $299 console marketed as a Blu-Ray player that comes with a BD remote, controller, 60GB HDD, 1 free PSN game, 3 free movie purchases from the PS Store, and media server software that allows you to stream music/videos/music to your PS3 from your PC/Mac. Then they can add a $399 SKU marketed as a midrange gaming console that comes bundled with a hit exclusive/"big hit 3rd party" game like Killzone 2 or LittleBigPlanet, a controller, and a mic. Finally, they can make an Ultimate Bundle with a $499 SKU with a 160GB HDD which is a combination of the 2 lower tiers with an extra controller.
5: Upgrading the PSN/XMB: Sony should really upgrade the PSN. To compare with Xbox Live, Sony should add Cross-game inviting, voice messaging, cross game chat system, etc. Also, Sony should fix some online stability issues. Online is not that bad though, it more than adequate.
The XMB should also be upgraded with a more intuitive and simple feel. Something like this. They can also add the feature of playing your music in game. Sony could also add Youtube and Hulu integration. (You can say that Hulu would render the PS Video Store useless but the Hulu player would have commercial intermissions in shows/clips).
Most of these features will be added in the upcoming 2.70 update.
Sony could also go out on a limb and make the PS3 startup on Home. This will either make - or - break the console because it will guarantee that people will use Home but it can also be buggy and laggy which can discourage some people to use the console.
6. Finally, ad campaigns: Sony needs to spread the word about their console. They have to abolish the old impressions that people have for the console. They need to stress the fact that it is also the BEST Blu-Ray player for the price. If Sony will make a price cut to the PS3, all they need is to do is emphasize it on an ad campaign. This could dramatically increase sales. Another way to potentially increase sales is to glorify the many exclusives that the PS3 has or has coming through all types of media, whether it be through gaming, tv, etc..
Sony really needs to go the offensive. If they do, this will help them win the console war...