A Google Groups thread confirms the sad news of Palm's future. Google has decided not to spend the time, money and resources to build out a new version of the Google Maps for Mobile specifically for the Palm OS.
Googler, Tom, from the Google Mobile team said:
I don't anticipate any new versions of Google Maps for mobile coming to Palm OS in the near future. I know this isn't news you'd like to hear, but the team has decided to focus their efforts on other mobile platforms at this time.
I assume, if Palm ever regains some popularity, Google would then develop more for that OS. But with Android, the iPhone, BlackBerry and other popular mobile devices - it seems like Palm and the Treo have seen their day.
Forum discussion at Google Groups.