* jokes
* complaints about downvotes
* downvote predictions (thus self-fulfilling prophecies)
* single word / single expression
* simply (dis)agreeing (there are up/downvote buttons for that)
* condescendence, insults, etc.
This is very different from Reddit where numerous threads end up littered with jokes and puns. On the other hand the following types of comments tend to get upvoted:
* insightful and well structured (as in: cut in several paragraphes)
* food for thought
* counter-point (politely worded, obviously)
* sourced
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Your first comment was probably mostly perceived as a joke:
* “ROFL” just expresses your personal reaction to previous information, and the common use of this acronym usually signals a low quality comment
* “Bootstrap has become a sign of a lazy developer”: this reads as both condescending (“lazy developer”) and unsupported; a more constructed argument with the same idea would have been fine
Your second comment contains the word "downvote", which is often enough to get downvotes.
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You might want to have a look at: