Screenshots are unhelpful. Please use a reprex.
As far as the general question of why
recall that R was invented, and has been extended and maintained, for use by statisticians for statisticians over a period 10 years longer than the existence of Google, beginning with the language S from Bell Labs in 1988. You've identified the source of the disconnect
median has an default argument of na.rm = FALSE because calculations involving NA evaluate to NA.
NA + 1
#> [1] NA
NA is not equivalent to 0 and shouldn't be treated as if it were.