Why are there 50 United States and the territories aren't included?

Territories are included in the Constitution as a Congressional power with most territories becoming States over time. Most remaining territories are islands with Puerto Rico being the largest.
Note that Washington DC is a federal district, not a territory.
http://everything-everywhere.com/2013/06/27/everything-you-need-to-know-about-the-territories-of-the-united-states/

I think it's up to the territories if they want to vote to become states. I was reading about it a couple of days ago. If I remember right they poll the population of the territory to see if they want statehood and if they do it goes to D.C. to decide whether or not to grant the territory it's statehood.

interesting thoughts... there are some that should be made into states and some let go on to be separate countries...