Can I ask why you think this is better? I just did some quick math, and based on the average yearly cost of incarceration for an Adult Male in Indiana at $19,202[1], assuming SBF lives for another 50 years, that's $960,250 of tax payer dollars being used to store someonne that contributes nothing to society. So after he's stolen billions of dollars, we'll spend another million keeping him alive for absolutely no reason whatsoever. It doesn't make sense to me economically or socially. It doesn't even make sense to me as an individual, as I'd much rather just bite the bullet than spend the next few decades looking at concrete walls.
[1] https://faqs.in.gov/hc/en-us/articles/115005238288-How-much-...
[0]: https://www.amnestyusa.org/issues/death-penalty/death-penalt...
It also costs a lot to go through that process and determine that execution is not justified, at which point we're still on the hook for imprisonment.
Putting somebody in jail for life is a bargain in comparison.
[1] https://www.leg.state.nv.us/App/NELIS/REL/76th2011/ExhibitDo...
Others are discussing whether your math is correct, but the fact remains: it's murder, we shouldn't be killing people, period.