You will find that very long focal lengths come only in 2", eg. from about 30mm or longer. Short focal lengths only come in 1.25", from about 15mm and down. Between these two you can get them in either size. The main reason for the large size at long focal lengths is that they need to be physically bigger to "fit the light in" as it were, especially with a long focal length of 30 or 40 mm and wide angle views of more than the 50 or so found in a Plossl.
If you only have 2" eyepieces, you won't be doing much planetary or double star viewing