Prisons cost money.
Prisons cost money.
As far as I'm concerned, there is indeed a punishment/revenge factor also in our current justice system, besides rehabilitation and keeping the streets safe from wrongdoers. That could lead to minimum sentences, especially for murder and even more so when it's premeditated. In general, I find that judges (in the Netherlands) strike an okay balance.
How much people live in Dutch? If Russians will send one killer for every key men in country, country will be their in just 12 years, while they lose nothing, because Dutch prison is much much more comfortable than a flat in Rostov. I see that in Ukraine right now.
In addition, convicts may be involuntarily committed when their sentence is over (and often before). This is aimed at rehabilitation, but can be extended indefinitely.
[1] https://nl.wikipedia.org/wiki/Lijst_van_tot_levenslang_veroo... (in Dutch)