It is weird how frequently the cards expire. I was quite surprised to visit Tokyo and have my Passmo card still working after not being there since 2009. (They expire 10 years after the last use.)
MetroCards are so cheaply made and thin that you'd be lucky if you can actually use one on a daily basis for a year without it becoming mangled or unreadable. The MTA probably enforces a one-year expiration to avoid the expense of having to deal with massive numbers of complaints about unusable cards.
Because of the unreliability of MetroCards and MetroCard readers, the MTA is planning to phase them out in a few years and replace their card readers with equipment that can directly read contactless (RFID) credit cards.
Octopus cards never expire, as far as I can tell.
The US is, not surprisingly, way behind here.