Hmm, there is no official reason why they stopped licensing, but it is obvious that the reverse imports of uncensored versions did hurt their home sales.
And for the date(s), depends if you consider the Japanese, the US or the Spanish release dates. A bunch of titles came out exclusively in Spain (Masaru 2, Houkago Mania Club, Flutter of Birds 2, Zankan, etc), with titles that had 2004 release dates in Japan.
2004 is the year when Pink Pineapple went bankrupt, at the same time they were celebrating their 10th anniversary, with no new releases between September 2004 and July 2005. They somehow revived themselves as if nothing had happened. The last licensed episode from them is Kusaku Spirit 3, released in Japan on 22.07.2005, but the series had started in 2004. The change of staff may be another reason why they stopped licensing new titles.
The same Kusaku Spirit was the last new PinPai license released in USA, in 2006 from Kitty Media. Well this is not really true, as we got Bondage Game a year or two ago. I think this one was a sleeping license, as the material itself was very extreme and risky.
Spanish company Llamentol went to release many adult anime DVDs in the 2000s, taking material from several japanese companies (PinPai, Milky, Five Ways, Green Bunny, Lemon Heart). But only some of the Pink Pineapple titles were exclusive outside Japan (including Bondage Game until it went into USA as well). According to my infos all the exclusive titles went out in 2005 and 2006, the last being the second volume of "Kawarazaki-ke no Ichizoku 2" on 27.10.2006. Llamentol continued with "hentai anime" DVD releases until 2008.