Large sedans do not sell like they used to, and tend to be bought by somewhat conservative types. The Intrepid styling is not anonymous enough for people like that.
Also, since Chrysler is no longer a North American company (and now poorly run on top of that), that has turned many off from buying one. May as well buy Japanese as Chrysler seems to be the idea.
The biggest problem for Dodge and Chrysler is general is they do not have a good reputation for long term quality and durability. Perceptions are more important than reality in this area. Bad reputations take longer to lose than it does to make a good reputation. The transmission and A/C problems in the early 90's Chryslers have soured many from buying another Chrysler product.
I have to say my 2000 R/T is light years ahead quality-wise of my last two Chryslers, an 84 Turismo and an 87 Sundance Turbo.
I plan on keeping the R/T past 100,000 miles, and if it craps out on me, there is a good chance it will be my last Chrysler as well. At 16,300 miles, so far, so good.
Of course, the new Neon SRT with the 2.4 liter turbo sounds interesting.