If they're deleted it's because they're not answers. Comments which fail to answer the question or are just 'joke' comments (e.g. all the stupid "[deleted] hur dur" comments) get removed.

Comments that answer the question and are of a reasonable depth don't get removed.

You aren't going to find answers among the deleted comments. I've been a mod on and off here for the past few years and I can tell you from experience that most of what's removed is trash, and the rest is basically copy-pasted from a google search.