If the men you are dating can't commit, it is because you are attracting and attracted to the wrong type of men.
Change your personality and observe what types of men can commit. Men who can commit are stable, mature and possibly interested in having children. That is, you might be attracted to men who are interested in flings, wanting to party and has no stability.
Another reason could be because you are asking too early. After a year of dating, it is ok. After a day of dating, you will scare him.
A third reason is simply because you need to push him a little. Commitment means loss of freedom to some men. This loss is frightening. A little push and he may surrender.