Every woman I've ever talked to IRL has stated that they hate unsolicited dick pics. Especially from men that they barely know or just met. Apparently lots of guys do this and it's just a quick way to get your number blocked.
Then, when it comes to online dating, it's very common for women to specifically state in their profiles not to send them. Based on my conversations with women there, most women there just block the men who do it unsolicited.
Then if you read any online dating forums such as r/dating or r/datingoverthirty, the overwhelming sentiment from women there is that unsolicited dick pics are a huge turn-off and they label the guy a creep and block him.
Based on this, it's perplexing to me that guys do this because it seems like a simple cost-benefit analysis would show that sending an unsolicited dick pic is just not worth it. If she was interested in you before, now she's probably going to block your number. It's a waste of effort. In my experience, women in general like more tact when it comes to relationships/sex.
Of course, there are some women out there who like unsolicited dick pics, but it seems that those are far and few between.