It's a bit hurtful that they would say "teenage laziness," when it could be depression.
It started when I was 12 (probably). I slowly started losing interest in doing things that I enjoyed, even more so about the things I didn't enjoy doing. By the time I was 15 I stopped caring about my future and from a straight A student I became a C/D student. When I started high school that I wanted (we have similar requirements for HS as you would need for college or university in Croatia) things were better for about a year, but I started to fade and become "numb" again. This continued throughout HS, but since my HS was mostly about sciences (physics, maths, computer science) and linguistics, so my grades didn't suffer because I found the topics interesting.
I am a freshman & 20 years old. I am doing better because I sought help, while everyone I lived with (mum and grandmother) thought I was just a lazy, worthless do-no-good. I should also mention that my mum has an "abusive personality," which probably contributed to my depression (and is hindering recovery, in all fairness).
I was lucky to have a best friend since kindergarten, who was observant enough to notice my mental and physical deterioration and supported me to find help (to paraphrase: "i will beat the fuck out of you if you don't get yourself checked for some shit").
I was diagnosed with MDD (Major depressive disorder). I wouldn't say I am good, yet, but I am better than I was a few years ago and I haven't thought about suicide for almost 2 months now (which I did, for 4/7 days, six months ago).
TL;DR: When you are depressed, it seems like the air is thick and heavy, it seems like every ray of light is trying to push you down onto your shadow, it seems like every movement you do is being countered by an invisible force and requires you to use more energy. All your thoughts are polluted with a dark tint. You have no dreams, no hopes, no desires. You just wish to escape.
Maybe they are not lazy? Maybe hiding in their rooms are the early attempts of escape, and nobody is noticing their silent cries for help.
P. S: Sorry for the long&sad post.