Hardware fails over time and gets increasingly less reliable and harder to source. These types of upgrades are mostly about maintaining existing functionality on modern hardware.
We might hope that at some point in the early 2100s, somebody will notice that none of the nuclear missiles work anymore, and with any luck, the engineering knowledge to create new ones will have been lost.
https://www.lanl.gov/science/weapons_journal/wj_pubs/17nwj2_...