This is, in fact, a billion dollar opportunity -- ads on porn sites are so abundant and so cheap, first person who will help sell more premium product by advertising it on porn sites will become a billionaire. Not happened yet, and most porn sites advertise, well, other porn sites. There might be a reason for that (and it's not a hidden cabal of puritans who run marketing departments of well-known brands being haters of porn. trust me, those folks will sell their souls to the devil for 10% uptick in sales).
In fact, as this generation of baby boomers dies off, I have a strong feeling porn will become far more normalized and have more prestigious non-porn brands associated with it, so long as more prestigious porn brands can rise up.
I mean current moves are more along the lines of dropping topless women from tabloids/Playboy ending nudity, Britain trying to age-limit porn, etc.
Also probably comes down to the basic technical difficulty of targeting ads on websites often browsed in private mode. Which will probably keep being the case for a lot of people, for practical reasons, regardless of how normalized porn might be.
I own a Porsche, I couldn't care less who they are advertising to so long as it doesn't hurt anyone. Moreover, I've learned with anything that attracts that much attention, it's not signaling any kind of attention you would want. I get really annoying attention, on a daily basis. If it wasn't for the tears of joy that I get from driving it down twisties, I would sell it in a heartbeat.
From my perspective as someone in the 1% of my age group and was apart of the set of young and dumb, vain and insecure people, signaling with expensive items is childishly overrated; it's far more fruitful to signal with kindness, compassion and intellect; any trust fund baby can afford a porsche and be as vapid as anyone else.