I sort of agree with you, but there can be a psychological advantage in psyching yourself up to make a drastic change at some specific date in the future. New Years is a natural landing spot if you wanted to use it in that way. I don't think it is appropriate for Lent since a person generally is only changing for that specific period.
Its not always only changing for the specific period of Lent. Sometimes it leads to a bigger life change. For example, I gave up pop for Lent 6 or 7 years ago when I was drinking 4 or 5 cans a day. I found it was a good encouragement to do something like that and made me realize I didn't need to start it up again after Lent. I do still drink some but only about 3-4 cans a week now. So I see that Lent sacrifice as more of a longer change.