Modern women won't mess with guys without being courted. Women now force most guys to buy dinner and other shit to fuck them. Chad is the exception. He has a perceived sexual market value above the woman and so fucking him is its own reward to them. He makes her completely lack self control sexually. Red Pill calls it the top 20%. I think there are some objective factors at play (BF%, build, height, facial symmetry, genetics, etc) but one woman's chad may not be another woman's chad, and chad can become not chad to that woman if he commits because it lowers his value as a male to be tied down to 1 woman, and even that 1 woman knows that. It's why men, even former chads, become far less attractive to their wife after marriage.

To put it shortly, chad is who she wants to fuck. She'll supplement lifestyle and money with other pathetic dudes that don't really turn her on, but chad satisfies the sexual desire.