Key management would be a nightmare here. IPSec has very long setup times, and every destination would need a new crypto configuration. This is exactly the problem that TLS was designed to solve, and IPSec and the web are a bad mix.

IPSec is a complex design by committee, with NSA's help. Schneier does not believe it will become a secure system.

http://www.mail-archive.com/cryptography@metzdowd.com/msg123...

https://www.schneier.com/academic/paperfiles/paper-ipsec.pdf

IPSec is beautiful and definitely was the correct way to handle encryption.

IKE and ISAKMP was the problem, that stuff is an absolute nightmare. Maybe now with IKE2 it might get better...