Nor is it hard for many(most)... our phones have been doing this (reliably, OTA) for 20 some years, computer systems have been doing this for (much) longer (the update gets delivered either OTA/over a network, or via some other process, then you press a button (run a job, etc) to apply the update... no significant difference)... all without anywhere near the rate of failures we see today with cars... the technology is well understood by some industries, and poorly by others. The technology fields in question (cars, phones, computers) just aren't that different, they are all programmable hardware systems (computers).