Firstly, Nofap boosts your fertility making you more attractive to girls on a physiological level. Many guys doing nofap report girls staring at them, flirting with them, etc. It is pretty simple, you aren't ejaculating and your capacity to make babies increases tenfold. Sperm lives in the body for up to a few weeks, so if you abstain for a few weeks then you reach your maximum fertility, and if you start ejaculating a bunch of times then the girls aren't going to be as sexually attracted to you as they would otherwise - they stop staring at you, etc.
And the second thing is that it boosts testosterone. I have read many accounts now of guys who have had their testosterone levels checked before and after nofap and it drastically increases, one case doubled his testosterone. I can also personally attest to changes in my voice, aggressiveness, confidence, etc, over time when cutting back on fapping - all indicators of a testosterone increase. So, naturally as a result you are going to be more assertive, sharper, and confident with women. You are more inclined to approach women.
I think its more of a shift over time. Like your body is ejaculating a bunch of times, less testosterone is required. You aren't getting laid so testosterone goes up. Maybe it is tied to your actual sex drive, who knows, but it works.