Why does mapply not store ggplot objects in the output

Question

When we use mapply in this scenario it will return the actual numbers that resulted from multiplying x and y:

mult.fun <- function(x, y) {
  x*y
}
res <- mapply(mult.fun, seq(1,3), seq(1,3)) # gives > 1 4 9

Then we can access the results later on using the list index:

res[[1]] # --> 1   (or just res[1])

I want to do exaclty the same however instead of numbers I want to store ggplot2 objects:

plot.fun <- function(x, y) {
  ggplot(data = NULL, aes(x,y)) + geom_point()
}
res <- mapply(plot.fun, seq(1,3), seq(1,3))

I thought this would simply store the results similar to the numbers, such that res[[1]] would give me a ggplot2 object, but is returns this:

list()
attr(,"class")
[1] "waiver"

When I call the function directly it will give me a ggplot2 object:

class(plot.fun(1,1)) # --> "gg"     "ggplot"

How can I call the plot function and store the actual plots in a list? And why doesn't mapply do this?