Because they help us through The Seven Stages of Love:
Stage 1: desire from afar: I want to Hold your Hand;
Stage 2: phew, confirmation it's mutual: She Wants to Hold your Hand;
Stage 3: bliss; 'going out': Here, There and Everywhere;
Stage 4: sex, lots of it: Drive My Car;
Stage 5: oh,oh: challenges : We Can Work it Out;
Stage 6: mutual respect and deeper love: Let it Be;
Stage 7: eternal love: Two of Us
Bonus: The Beatles did actually produce an album of love songs, sadly never released on CD (not to be confused with the recent compilation 'Love' album) and clearly not available on iTunes. But you could create one for your loved one for Valentine's Day. But don't forget the single rose tied to their bicycle; that's the bit most people don't do.