Lemmy

50% response rate doesn't sound too bad. a) People don't owe you a reply, as you already said. b) Accounts go dead. Sure, when offering mod positions you probably didn't contact many accounts that posted once a month ago, but still, many may have tried out multiple accounts on different instances, Lemmy vs. Kbin etc. and at one point decided for a different one, or they went back to Reddit, etc. c) DMs may look like spam or phishing or continuation of long abandoned discussions, and so some DMs will go unread even though the receipients saw the notification. d) people forget to answer, or they may want to think about the reply longer than you would expect. e) people are lazy.