No need to be repentant when you are innocent.
If they aren't executed, they will spend the rest of their life in jail. So by executing them our gains are two fold.
1. save tax dollars over keeping them in jail long term
2. give victims families peace
Something to think about.
Additionally, there are the questionable convictions and the legal convictions that are subsequently found to have been innocent but for which innocence is no longer considered (e.g. dobbsbob comment about Rob Will - https://news.ycombinator.com/item?id=7822471).
In many states there were mandatory appeals for death-row inmates which added to their costs. For most other sentences there were more limits on appeals which in-turn limited the life-sentence appeals costs.
There were higher housing costs for the death-row inmates, although I don't remember seeing a breakdown. I always assumed the differences were because of increased security costs. The housing costs were for entire expected sentences, not by year (while a life-sentence inmate would be expected to need housing for a longer time, the costs were still less than a death-row inmate's costs until execution).
Also, in many prisons, the life-sentence inmates could participate in work programs, with some of the related income being funneled back into the prison. At the time I was doing my research I couldn't find any work programs that allowed death-row inmates to participate. So not only were the life-sentence inmates cheaper, they could potentially work to reduce their own costs.
We might differ in opinion on the role of government, though. Personally, I don't think either task is the job we want our government to be in.
The common response to this is something like, "Well, make it cheaper. Stop with all the appeals and other nonsense." The trouble is that we already execute far too many innocent people, and streamlining the process will only make it worse.
To carry out executions in anything resembling a just manner, it pretty much has to be more expensive than imprisoning someone for life.
As for #2, life without parole should be just as final as an execution as far as closure for the victims is concerned.