That, in and of itself isn't bad, nothing wrong with always picking gambling when you have some free time and money.

With addiction, of any kind, it kind of creeps past the point of free time and money. Preferring X over sleep, work, food, whatever other things are important is where it gets pretty rough for people.

So anyway, yeah, there's an element of personal choice. When the biases get so strong, it's hard to recognize that a choice is even being made. People don't exactly choose to brush their teeth in the morning, it's just something that happens as part of the morning routine. It's technically a choice, but the bias is so strong, people rarely consider not brushing their teeth. (as a somewhat silly example)