To an extent the parties control how long a divorce proceeding will last. Some couples want to separate their personal and financial lives, but not finalize their divorce for some reason or another and so take their time finalizing their divorce.
I have worked with some couples with major debt and tax problems who need to resolve complex bankruptcy or tax issues while still married but living apart and so the case remains open for several years until these other matters are concluded.
In one case, the couple had started a major remodel and then decided to divorce, but they could not sell their house until the remodel was concluded and they had to mediate major decisions in the remodel in addition to the typical divorce matters.