Is that being a bit sneaky, or catching customers who don't read properly and just sign on the dotted line?
A bit of both I suppose.
The business models are different. Say for ST or SH, just charge full price and rip off everyone. What they give is highest priority on their network, 5G, 24/7 hotline, but not necessarily the most data. They also give convenience.
Whereas for the cheaper MVNOs, there is always some catch. Nothing comes for free.
An MVNO like heya or Eight makes money off people who aren't that careful, or not really that OCD. I don't really like this business model as it makes money off people who make mistakes, but it is what it is. Similar to Groupon; while they existed, they made money off people who bought the vouchers and never used them.
As an example, I know someone who signed up for a new line in August, forgot to key in the EIGHTNDP24 promo code, so he was only give 30 days free. He then itchy hand went to recharge the Double Eight plan on the second day without reading the T&Cs clearly, thus overriding the free plan (he thought it would queue up after the free plan ends). He ended up getting only one day free.
So, Eight makes money off people like that, and that's why I don't really like this business model. Nothing much we can do about it I'm afraid, except to try to be careful ourselves.
And yes, Eight is actually quite smart to do this, as everything is above board and nothing they do is illegal.