The reason only 28 books of a planned 32 were published, and the 28th remained incomplete.
And as mentioned above, the later books were shortened in the US for no apparent reason. Project Aon features the full UK versions.
Uncancelled: An effort to give rebirth to the series was begun by Mongoose Publishing in 2007, where they would reprint the books in hardcover with new art and new bonus adventures. They made it through seventeen books before circumstances forced Dever and them to part ways in March of 2013. The series was almost immediately picked up by Mantikore-Verlag who have pledged to print up to book 28. No word yet if M-V is publishing the last four intended books. Or if you can't wait, head to the aforementioned Project Aon.