The 32-bit computers are the only thing available to lots of poor people or those just relying on other people's computers. People's teenagers, people using libraries, workers with legacy systems, and Internet cafes come to mind. Dropping it is a mistake if both could be supported. If it was lack of contributions or funding, I can understand the perspective of focusing on most secure one.

EDIT to add: Always remember with solutions like this that the adversary isn't always the NSA and so on. The Tor users' page lists all kinds of people who need help against foes with limited budgets or knowledge who might not be able to break Linux or Tor.

https://www.torproject.org/about/torusers.html.en