When casual sex is a possibility, many high value men will see it as a desirable option to commited relationships. And since for most men, their standards are very low for casual partners, they're willing to date far below their "level".
That puts women in difficult position because the most desirable partners are far more likely to be looking for only casual sex. But even if women adopt strict strategies to filter out the desirable men who won't commit, the men will naturally adopt deceptive strategies to evade detection as a "fuck boy".
When potential partners largely came from your real social network, the social cost was high for men for "using women for sex" and for women "being easy", so that prevented this problem to some degree.
Now that partners largely come from outside our social networks, there doesn't seem to be any good way to reproduce the social shaming for deceptive non-commitment.