I think there are quite a few reasons for this. Starting that to the majority the concept is still quite unclear but with the right incentive people try to sign up. Here they bump into another roadblock which will be hopefully removed with Velocity hardfork and effortless on boarding. And some users are waiting for a week or more for their account to be approved.

I know this because we have connected our photography platform BeScouted to Steem blockchain and are bringing new talented authors to the platform. Here they the bump into underlying Steemit problem. New members despite the effort from many older active Steemit members get too little attention and their rewards of 0.01 or 0.02 cents per post looks funny having in mind it is in a currency they yet do not understand. So the strongest marketing tool "word of mouth" doesn't even kick in. Even those who are determined more and stick longer lose motivation over time. Hence leaving the platform later on and then they are telling everyone that on Steemit only the whales or those who are in auto vote lists earn reasonably. And do not get me wrong, it is not the low earnings that discourages people, but seeing really shitty content in trending tabs with hundreds of dollars. And this is not my personal opinion, this is the feedback from the community.

@bescouted.com has some delegated SP which was delegated by a few really kind Steemit users, who want the platform to grow. The rest just keep renting it for a few bucks failing to understand that if Steem price does not multifold those few bucks they are getting will not save the day and will not take them to the Moon.

It is naive to think that it will change and gets me a little bit worried, since in it's core Steem blockchain has very powerful potential, so i hope things will get much better after communities are able to release their own SMT's and apply slightly different reward mechanics in the apps that they build.

So you understand that getting users on Steemit is just one side of the coin, and spending money to get paid traffic is a waste of money if it does not stick as LTV becomes extremely low and even people who are on the platform for a longer time leave or become exceptionally inactive.
Considering your effort you are doing a very important job, and it is nice to know you have funds to spare for doing this. If there was only more people like you i believe we would see a completely different picture. And all recent disruptions in Steemit technical operations recently did not help either. It's much better now, and lets have our fingers crossed it remains the same. As getting people on a platform that is not functioning is extremely problematic.