Cannot fg a zsh function including less

I have this zsh function:

f() {
/usr/bin/find . -type f | less
}

When I run this function, suspend with Ctrl+z, and then run fg, it displays zsh: suspended (tty output) /usr/bin/find . -type f | and I can't resume. Why is that? How can I resume?

arch% f
zsh: suspended /usr/bin/find . -type f |
arch% fg
 - continued /usr/bin/find . -type f |
zsh: suspended (tty output) /usr/bin/find . -type f |
zsh: suspended (tty output) /usr/bin/find . -type f |
arch%

If I run /usr/bin/find . -type f | less directly from the command line without making it a function, it will suspend and resume normally.