No one is jealous of bad spelling and grammar, or cliche plots.
I do not often critique the work of new writers, especially here, because they frequently take it personally (age has a lot to do with that here - teens tend to take everything personally). My critique style often seems harsh, even when I mean for it to be encouraging (knowing that about myself, I try to be careful when I do offer a critique).
It takes a little bit of getting used to criticism when we bare our souls and ideas (and dreams) into something and someone else spots a problem or twenty. New writers of any age just haven't gotten enough scars yet, so it hurts a lot more. Experience will guide you in knowing which critiques have value regardless of the tone they are given in. A fair amount of scars and experience will make an agent's or editor's critique a lot less painful (trust me).
I am very rarely outright mean to anyone. They have to come across as being deliberately obnoxious and in need of a good dose of reality, or just a troll looking for attention, before I leave a smart*** response.
Unfortunately, for some people on here, their form of entertainment is to cause pain. That isn't from jealousy, it's about their already poor self esteem. Like any other type of bully, they have to belittle others in order to make themselves feel artificial self worth by having the power to hurt others (and there is nothing quite as satisfying in writing as proving the bully wrong when you do get published - you can trust me on that, too).
Writing, in general, seems like an easy thing - everybody has ideas and can tell a story - so many people who do not know how much craft is really involved will devalue it and the author.
When the new writer is starry-eyed about wealth and fame, yeah, a lot of other writers are going to snap at them. Writing is work, fame and fortune are fleeting, goals need to be achievalbe, and it does not help the perception of the art to let people gush on about unrealistic dreams.