There's been some increase in comment deletion, but there's context.
Comment flags (per week) for the last year:
The shape of that curve isn't unique to The Workplace; it's similar on Stack Overflow, though of course the Y-axis values are different.
Are people flagging lots of old comments and that's why we have a problem? To answer that, here's the percentage of comments posted each week that got flagged:
The shapes of those curves, especially recently, are very similar. That suggests to me that the flags are mostly on new comments. So either we're getting more flag-worthy comments or people are flagging more aggressively; either way, if moderators delete the comments, that means we felt the flags were warranted.
Even with more flags, though, moderators aren't purging tons of stuff. Other things have happened too:
In the last year, 72,761 comments have been posted here, with weekly totals mostly ranging between 1250 and 1750. 15,925 of those comments have been deleted, about 5600 of them by their authors (not moderators). 6409 comments were moved to chat and thus preserved (in 391 separate threads). Some of the comments moved to chat were not also deleted on the main site, so I have to get a little hand-wavy on that part, but at a rough guess, out of those ~73k comments, only around ~4k were actually purged. The largest flag reason by far was "no longer needed".
We get a lot of comments and a lot of flags on comments. We relocate a lot of discussions and about a third of the deletions are self-deletions. Moderators are outright nuking fewer comments than you seem to think we are, and the process is substantially driven by flags.
(Thanks to Shog9 for data-wrangling.)