Not one, since every 1 possibility has been listed but these are what I think matter the most to me.
Women have an upperhand in a lot of ways these days, in the US, so start acting like it. Women can flirt and ask guys out at random more than the reverse now, guys worry about the high odds of rejection plus being labeled a creep and ending up on someone's Twitter feed, so we've pulled back a lot on that but most of us like it when women flirt with us, it just rarely seems to happen (unless maybe the guy is a complete 9+/10 stud). If you're ignoring guys, not flirting, acting cold or like a guy is a creep if they dare show any signs of interest (and aren't 100% your ideal type), you're not helping yourself or the current dating problems.
If you're participating in online dating, please be realistic and also not treat the men on it who aren't complete studs like they are pathetic losers. It's very clear now that guys are very generous with their right swipes, including the hottest guys on it. You can kid yourself and think something is going to happen with one of those guys because they swipe right on you or be realistic, at best they'll hook up, but many will have too many matches even for that to happen. The odds are extremely low they will want to seriously date.
Some guys are being more cautious now due to the possibility of misreading something and being blasted on social media as a sleazebag or worse, being labeled a rapist and possibly being in a world of hurt as a result. Just be aware of that and don't think, "what a lame-o, they are not pushing hard enough to have sex with me asap, there must something must be wrong with them."