For me the reason is easy, there is simply no real benefit in powering up anymore. Right now when you would start a new account with an investment of <100SP and just make all the quick daily garbage shitposts that get the upvotes (Actifit/steemmonsters/esteem/...) and no engagement you would literally do 10x better compared to investing 10k+ SP and having a genuine blog on Steemit engaging on the platform.

In the end, people just do what's most profitable. When all money goes into steem-engine tokens along with steemmonster cards and such, it sucks the life out of the Steem price as it has just become a coin for making transactions and nothing more.