Why did I get a transaction fee?

Excuse me, could you clarify why I was charged a transaction fee when I made my recent cryptocurrency transaction? I understand that fees are common in this space, but I'm curious about the specific reasons behind it. Is it because of network congestion, the complexity of the transaction, or perhaps a combination of factors? I'd appreciate it if you could elaborate on the factors that contribute to transaction fees and how they're calculated. Thank you.