Laser hollowness. Why does it happen?

Why do lasers cause hollowness? I see doctors saying it promotes collagen, when in fact many people complain it made them look hollow?! I understand it's a money making business (that's why you're probably all going to defend it) but please answer honestly, And don't tell "it can't be" cause I see many people complaining about it (and in fact thermage is aimed at getting rid of fat, so again please don't tell me it doesn't happen) Thank you!

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