Why is there a fee to transfer money?

Excuse me, but could you elaborate on why there's a fee associated with transferring money? I understand that transactions involve processing and security measures, but what specific factors contribute to the imposition of these charges? Is it simply a matter of covering costs, or are there other underlying reasons that drive the need for such fees? I'm particularly interested in how this principle applies to cryptocurrency transactions, as they often tout lower fees compared to traditional financial systems. Could you shed some light on this matter?