Why Do People Eat Unhealthy Foods When They Know Is Not Good For Them?

Because humans have this wonderful thing called choice.  They also don't think about consequences too often.

Time restriction, late work hours, convenience, laziness and marketing. Yes, marketing. If people will buy a 7 dollar paper cup of coffee from starbucks, when they could've started a pot of coffee while they were getting dressed for work, they will darn sure sit in a car, talk to a menu, order a $1.00 dbl cheese burger instead of wasting precious time cooking an actual meal. How sad is that.

As somebody once observed 'All the best things in life are either illegal, immoral or fattening !"

Wouldn't it be great if a scientific study reported that cream cakes, or french fries were good for you?!
Can't see it ever happening, sadly.  Ah well  -back to the brown rice and salad !

It's addicting

Because they taste so good or they are in a hurry and fast foods tend to be fattening.

Probably because it tastes really nice and dont know what the consequences will be or they might just have cravings or something like that...

Called habit.. Once you try it SOME get hooked with it... Faster, delicious and satisfying..

Because junk food usually tastes better then healthy food.....so it makes people want to it more without thinking about the consequences. Then they are addicted to the food so they want it every day. Sometimes people eat junk food because it's most convenient for them...it doesn't take as much time and doesn't cost as much!