R vs sed regex greediness

I don’t quite understand why this doesn’t result in "test" and would appreciate an explanation:

a = "blah test"
sub('^.*(test|$)', '', a)
# [1] ""

Compare it to the sed expression:

echo 'blah test' | sed -r 's/^.*(test|$)/1/'
# test
echo 'blah blah' | sed -r 's/^.*(test|$)/1/'
#

Fwiw, the following achieves what I want in R (and is equivalent to the above sed results):

sub('^.*(test)|^.*', '', a)

You need to mark the ^.* as non-greedy

> sub('^.*?(test|$)', '', "blah test")
[1] "test"
> sub('^.*?(test|$)', '', "blah blah")
[1] ""