Compared to working with iptables, PF is like this haiku:
A breath of fresh air,
floating on white rose petals,
eating strawberries.
Now I'm getting carried away:
Hartmeier codes now,
Henning knows not why it fails,
fails only for n00b.
Tables load my lists,
tarpit for the asshole spammer,
death to his mail store.
CARP due to Cisco,
redundant blessed packets,
licensed free for me.
pf has been ported to Debian/kFreeBSD, but afaik no effort has been made to port it to the Linux kernel. A lot of networking gear already runs a BSD kernel, so my guess is the really high-level network devs don't bother because they already know BSD so well.
Nftables has improved the situation on Linux somewhat, but PF is incredibly intuitive and powerful. A league of its own when it comes to firewalling.