Comments are designed to be temporary clarifications about specific questions/answers and as such are cleared at regular intervals.
As the Comments privilege page mentions
- Comments are temporary "Post-It" notes left on a question or answer.
Comments are not recommended for any of the following:
Suggesting corrections that don't fundamentally change the meaning of the post; instead, make or suggest an edit;
Answering a question or providing an alternate solution to an existing answer; instead, post an actual answer (or edit to expand an existing one);
Compliments which do not add new information ("+1, great answer!"); instead, up-vote it and pay it forward;
Criticisms which do not add anything constructive ("-1, see previous comments you scallywag!"); instead, down-vote (and provide or up-vote a better answer if appropriate);
Secondary discussion or debating a controversial point; please use chat instead;
Discussion of community behavior or site policies; please use meta instead.
