Well Jack may have gone there.. but it was only after he had been to her..He was lost and wanted help from her...If he knew he should have gone to Tortuga in the first place then he would have gone there with out seeing Tia. Also she may not have been the direct reason he went there but she IS the reason why Will got separated from Jack..so then the JAck/Liz thing could develop and Will/Liz's relationship can then start to Mirror what happened to Davy Jones and his fiance.
I'm a film studies student..We are taught to realise that everything you see in a movie has purpose..the Jar of dirt simply being Tia's way of making Jack feel better would be completely irrelevant to the plot. It would be pointless...even if it was just to make jokes it still wouldn't need to be in there if it was just a placebo..
I'm pretty certain that its the reason why Norrington got the heart and Tia knew from the very beginning that it would be the way for Norrington to get it to the EITC. Norrington would have never found it had jack not put it in there...Jack would have still had it in his shirt and he could have killed Davy..but I don't think Tia wants Davy to be killed..so how can she prevent him from being killed? By getting the heart to a safe place..the EITC. Jack and Will cant get to it to stab it can they?..So Davy is safe for the moment..I think Tia is tricking everyone....
We have already established that there are 2 enemies Davy Jones and the EITC..there NEEDS to be a new one in the next movie to keep people interested in the plot..and the twist is that it may be Tia. Seo Feng wont be a big threat..he apparently dies pretty early on
after kidnapping Liz..
The pirates movies are all about people switching alliances. The director has given away the fact that the next movie will revolve around people constantly switching alliances..I feel that the EITC and Jack might join up in order to stop Tia/Davy. Jack/Liz will need their help to stop tia from making Will from become the next Captain of the Dutchman..and the EITC will probably need Jacks help to stop Tia being in control of the sea or what ever..
This is just a theory though. Based on what I have seen and what we have been told is going to happen in the next movie..