Say a couple enters a covenant marriage, and 5 years later they realize they didn't know each other that well before, and perhaps they are not meant for each other (it happens). Again, what good could come from making it difficult for those people to end their dysfunctional relationship? You think because the law tells you, you can't divorce, that the love is magically rekindled?
Yes, you could say "well, if people want to be able to divorce each other with ease then they can chose the normal marriage". However, lets face it when people decide to get married, they're not thinking about divorce! Its not like couples rationalise the possibility of divorce before professing their love to each other.
Forcing people to stay together simply to maintain the "family unit" is not going to solve a thing IMO.