When I looked into it, very little of the Helium miner payouts were coming from people using the network. Most of the payouts were from the network minting HNT to reward node operators, which they then cashed out by selling HNT to people on exchanges.
The obvious problem is that this model only works as long as the speculative value of the HNT token remains high. Once the speculative demand for HNT disappears, getting actual cash in exchange for mining operations is going to become very hard. Supposedly the operators planned on having actual end users pay to use the network, but that demand has been minimal so far.
They also had some problems where people discovered how to game the system and extract a lot of the rewards without providing much actual coverage. I don't know if they overcame these or not.
Like most crypto things, being early to the speculative game was the only way to make money. I suspect a lot of late arrivals who haven't even received their backordered miners yet are going to be in for some losses.