I don't understand...

How a parent can just walk out of their child's life without remorse. I have seen it and feel sorry for kids because they are missing out. I was raised by a single mother and I found out my deadbeat father passed away. I wonder if he regretted not being in his kids life. (He had a ton of kids by different women.) I also noticed fathers that get their children's names tattooed on them usually don't stay in their kids life. From what I seen. Just wanted to be random. What are your thoughts?