Why don't monks get married? If there are no restrictions in Buddhism then why do they not want to get married?
Of course there are restrictions!


  Abrahmacariya veramani sikkhapadam samadiyami (I will refrain from sexual activity)


If you can't have sex, your spouse probably won't be too pleased.  Having a family of your own will also prove slightly more difficult.  Besides, the whole point of forgoing the householder life for homelessness is to pursue enlightenment with the minimal amount of obstacles possible.  Supporting a family is quite a large responsibility to undertake!

(Note: this does not apply to all Buddhist schools.  Zen monks often marry.  But if you are looking for the strict, scholastic answer, see above.)