Considering why this would be so, I come to a few possibilities: firstly, that the kind of love in question is a "player's" love, where one is just trying to get as many mates as possible and overall the formulas help one to accumulate hits. However, given the use of some of these formulas (particularly Black Cat) in reconciliation workings and in fidelity spells, that seems a bit unlikely.
The next possibility then is that they don't particularly influence gambling or love, but rather Luck in general. The Church of Good Luck talks of influencers on the matter: "The mechanism by which these techniques operate is not known. Perhaps they serve to alter attitude or openness. Maybe they work in small ways on cause and effect to alter results in a larger way.Since the effectiveness of these techniques can be neither proved nor disproved theories are rather useless and practice is the key to results."
Finally, if you follow the practice of deity worship, there's the chance that these formulas particularly appeal to one of those Ochun/Venus sort of entities who rule over both love and money. In fact, it's slightly common in world religions that a single entity rules, or at least influences, both these matters -- Hariti, Kurukulla, Xochiquetzal, etc. In the case of Hathor, she is described as a "goddess of joy" and I suppose, given that love and money are the things most people worry most on, that makes sense.