"I can answer this! According to various sources (mainly, complaints on the redesign subreddit), the new.reddit interface is a lot less tolerant of timeouts and delays. Old.reddit was much more relaxed and would wait longer before throwing up errors (like logouts and such), but new.reddit is RESPONSIVE!, and the backend isn't playing nice with the new, tighter tolerances."
Even if it were truely the reason (it's just someone uninvolved who saw a lot of complaints about the new interface) it doesn't explain the rest of the decade where there was no "new interface" and it was still a meme that Reddit was constantly down.
Is that the way 'responsive' is being used in this particular context? What does reflowing a webpage when the browser's window changes size have to do with these timeouts and delays in the backend?
theres some ironic use of the word in the post above. they are mocking that the new and improved "responsive web" site isnt responsive in a speed context.