Some writers just don't care what readers think about their work, others turn off comments because they're tired of being trolled.
It's one of the tools the site gives writers, along with the ability to delete any comment the writer doesn't want. An analogy I used a while back - being able to block and delete comments is a way of keeping a tidy garden.
Contrary to what you might have expected, I will not leave unasked for "your writing sucks" comments directly against a story - I'm all sweetness and light. It's only here, where writers come begging, that I'm occasionally less kind. It does no-one any good to only receive flim-flam flattery when writing has its bad moments.
There are also those who wonder why they constantly receive negative comments - the clue is in the constancy. Some folk do need to pay attention, let's face it.
Whereas you, for example, walked through your baptism of fire with your head held high and I suspect you're a fast learner. Your next piece will be immeasurably better. Also, in the correct category, that's important