They really didn't say why. All they said was, "The Microsoft adCenter Analytics team announced today the end of the adCenter Analytics beta program." Current users can continue to use the service until December 31, 2009 but are urged to export their data to one of the many analytics packages available and cease using Microsoft adCenter Analytics as soon as possible.
Our team would like to sincerely thank you for your participation and your invaluable contributions to the program. Our objectives at the outset were to serve the needs of small and midsize self-service customers, as well as evolve the Microsoft strategy to address the Web analytics space.
The insights you’ve contributed through your feedback and your use of the tool have served an invaluable purpose in shaping Microsoft’s future in this space. You’ve helped us work towards making an informed decision about building a general Web analytics solution, and despite the end of life plan, the beta was very much a success.
It enabled us to confidently determine that we can be of most value to advertisers and publishers by offering a tailored solution that meets more specialized needs.
Then they listed a number of companies offering analytics, including Google.
Forum discussion at DigitalPoint Forums.