Because the license for Pine does not allow any binary distribution, Debian, Ubuntu, and probably others make the source package available, but not a ready made binary. 
To install it, create and cd to a new directory, then:

  apt-get source pine
  apt-get build-dep pine
  apt-get -b source pine

This has apt download the source for pine, then install any packages needed to build the package, then build (-b) and install it.

NOTE: You may first need:
  apt-get install dpkg-dev