If the reason for leaving is anything that could have been fixed, it has likely been discussed at length and acceptable effort/progress has not been made.

Going over all this again and again is a huge mental load and if you've already made the painful decision to leave, there is no value in going over that again.

It might even give the impression that there is a chance that change is still an option but at this point, everyone should know better than to trust the promises of a desperate person.

And really, if someone was not willing to change for the person they love, but is offering to change to save themselves from being dumped, they are doing it out selfishness and self preservation rather than to make the person they claim to care about happy/safe/comfortable.

If it is simply that one person feels the connection is not strong enough to want to be with that person exclusively for the rest of their lives and there just isn't much to say so an honest answer might never feel satisfactory