Another number sequence puzzle is the most downvoted question here.
It has 0 upvotes and 15 downvotes.
Can anyone tell me why the community thinks this is a very bad question?
The first piece of advice in the top answer is to search OEIS for the sequence, because if the puzzle is easy to solve by a quick OEIS search, then it's likely to be an uninteresting puzzle and people will probably downvote it.
As Gareth notes in his answer, voting is very much a "luck of the draw" thing - some bad or easy puzzles have been ridiculously upvoted, while some real gems have been mostly overlooked. The HNQ list only exacerbates this problem. However, look at the tooltip for the downvote button:
This question does not show any research effort; it is unclear or not useful
This was of course designed for sites unlike Puzzling, where questions reflect an actual problem the OP is facing, rather than a challenge to which they know the solution. But "does not show any research effort" roughly equates to "the answer is easy to find with a minimum of research effort". (If the answer isn't easy to find, then it's less important whether or not the question shows research effort, since that wouldn't be useful anyway.) If the OP's problem is easy to solve with ten seconds of Google, then it's likely to get downvoted.
We can apply a similar principle even here on Puzzling: if the OP's puzzle is easy to solve with ten seconds of Google, then it's likely to get downvoted. For number-sequence puzzles specifically, replace Google by OEIS, as the best resource for finding number sequences.
Also, it's worth noting that this isn't the most downvoted question on Puzzling - it's only the most downvoted extant question. Many more downvoted ones have since been closed and deleted. See for example this question with a score of -16 (+21/-37). Mods will be able to find more using this search, but I don't remember any offhand which I can find links to.
I think there's a large element of luck in exactly what votes a question gets.
But the main problem with that question is that if you take the list of numbers given and plug it into the search facility on OEIS, you get the answer.
Most likely the person who asked the question didn't know about OEIS, so it's not really their fault. But a question that you can answer by means of a single search in the "obvious" place isn't a good question.
(There have been plenty of worse questions than that one, but probably a lot of them ended up deleted.)