For users, is it simple just about monetising their banner space or are there any other reasons?
Nope, I don't think there are any deeper reasons than people just trying to make money.
It is very sad to see a handful of these users without any morals using any words they can trying to justify them promoting a tainted brand and for what? Just a few pennies...
This whole investbox thing has left a bad taste in my mouth since I've had some time to actually think about it. I don't like how Yobit changed their campaign signature from cryptotalk to the investbox one, which is asking members to advertise something completely different and at the very least smells very fishy.
People might very well be tempted to buy some of those non-existant shitcoins with "investment plans" on Yobit, in which case they're probably going to lose money when they try to sell those on the market after Yobit ends the plan earlier than the person thought. They're only going to let you earn 5% interest daily for a few days at most--and notice how you can't withdraw any of those coins or even find much info about them. It's all a load of crap, and any lingering respect I had for Yobit has basically flown out the window in the past week.
I was never impressed by them and what they had to offer.
The investment plans are a great way to maximise them receiving user funds and then leave the option for them to either exit scam their way out or stay put and tell investors their investment failed.