@hisnameisolllie had a steemit statistics post a few weeks back discussing the same thing. He believed bot posting reduction was a large factor, add in some of the people who joined during the large spike leaving due to low rewards and it makes perfect sense, nothing to worry about, the explosion will come soon.
Good to also see measures taken against name squatting, how is kanye going to have his 7 figure post if someone has @yeezy @kanye @kanyewest @yeezus and all his other pseudonyms controlled already?
Besides programmatically handling this.. implementing similar "username" squatting combats, similar like Twitter utilizes to handle the issue. Trademark and verified celebrity accounts could potentially be transferred especially if the account is inactive or being used to impersonate someone.
There is no limit to the name variations people can use when joining a new platform if they don't get there early enough and don't want to pay a squatter for a vanity name. This is about as big a problem as running out of numbers.