From the questions I have answered in recent times, most are from ladies who have to deal with why a guy who will not commit more to a relationship. Most of my answers boil down to one of the following four reasons. In short, guys have little incentive to commit to a lady over the long-term.
1. Sex Has Become Easier to Obtain
Today, ladies have greater control over their bodies and life plan via contraceptives. So it can be concluded that contraceptives have done wonders to improve ladies' quality of life relative to the past. The only unfortunate side-effect is that guys don't value commitment as much as they did in your grandparents' day because as much as one lady is willing to hold out, another one is DTF after a few drinks and some jokes.
2. Ladies Don't Need a Man's Resources
There's nothing sexier than walking downtown and seeing gorgeous professional ladies in suits and scrubs. These ladies make their own money and determine their own destiny. Therefore, (unless he's oozing money) guys make the logical conclusion that, "she doesn't need my money; she has her own." It's why so many guys refuse to pick up the check on a date and creepers are mostly the only guys waiting buy a girl a drink. Guys think, "she has a job, she can afford it."
3. Ladies' Negative Responses to Domesticity
It's been my experience that ladies are very reluctant to please guys outside of the bedroom because of a fear of being subjugated in a relationship. This is hard to say, but guys still like it when ladies make sandwiches for them, and they still like it when they don't have to pick up after their lady after she walks out the door. The vast majority of the ladies I know cannot cook well (if at all) and live just as dirty as many guys I have encountered, yet refuse to cook or clean because they vehemently oppose being domestic. A lady like the ones described in the previous sentence would be viewed by a guy as (1) being unable to take care of herself (she cannot feed or pick up after herself) and as (2) a liability (now he has to feed and pick up after this her).
4. Divorce Laws
If a guy is dating a lady for an extended period of time, then the lady will inevitably want more commitment in the form of a title, usually as a wife. The lady's desires are reasonable, born out of personal and societal expectations. But a guy will be forever reluctant to submit so much control of his life over to one lady, even if he loves her at the time. He could lose half of his possessions, his children, and decades of his life simply if she changes her mind about how she feels about him. Many men figure its best not to go down that road in the first place or to ride the friends with benefits phase of the relationship until the wheels fall off.
Therefore, if a guy commits to a lady he will (1) forego sexual opportunities for which he may have needed to invest relatively little; (2) he will absorb a disproportionate chunk of the financial strain of the relationship; (3) he will take on domestic roles not only for himself, but for another person as well; and even it all works out, (4) he may lose his things, his children and his sanity over a woman's change of heart. So. . . netflix and chill?