The first reason is basic conservatism. There will always be an objection and it's safer to avoid. Otherwise, many parts of online advertising form a very comp

The first reason is basic conservatism. There will always be an objection and it's safer to avoid. Otherwise, many parts of online advertising form a very competitive market and if it was valuable (eg you can find customers this way) there would be demand. It just doesn't work well (yet). Users don't trust porn sites.