6's population has been declining since CEVO at least
we've finally hit the point where all the people who joined before then are starting to quit so its really noticeable now
you're also seeing the thing where no one new joined the community between like seasons 8 and 10 so there was this weird power gap a year later of upper invite and everyone else cause no one new had joined and gotten better but it took a year to be visible
edit for clarification: 3rd paragraph is an example. Platinum I think mentioned once how marmadukegrylls was like the only player in invite who started playing between a certain period before the f2p update. You had a decent amount of older players from the beginning of ESEA and shit and a few who had gotten really good from seasons 12 on but there was this weird gap where you had basically no players who had their first season. I think the CEVO/ESEA split drove away a fair amount of people and you started to see the people who were low/mid open back then (people on my teams) finally start to really get into IM/Invite within the past few seasons. I think the CEVO/ESEA season (and the ones leading up to it) was the last time 6s really got a strong surge of players interested in 6s/ESEA so now that we've had the big population boom finally reach their "endgame" we're seeing how the population growth started to taper off in the past two years. Even if interest in 6s grew to CSGO levels in the next month you'd still have a good 12-24 month turn around before we started seeing people really hitting ESEA hard. If ESEA doesn't see a slight increase in interest as a result of MM in the next few seasons the game is probably on its final downslide