I think it also has to do with the total hashrate.
For example I mined 0,05 Ethereum 1 year ago with the Rx480 and it took me longer then a month.
Because The Total hashrate was a lot higher a year ago, so it could be possible now that miners are receiving more ethereum.
But I do think people do it because they actually believe in Ethereum and they wont just quit after one period where the market goes down.
Hashrate is not only the main factor because you have been forgetting to mention the impact caused by the block decrease. Did you know that if this will be giving a huge impact on the result on how much ethereum that will get by the miners even if the hashrate gets less than a year ago? you can't get it because it has been getting a halving that reduces ethereum block reward from 3 to the 2 per block. Hashrate power is not the only thing that affects ethereum supply and rewards to the miners.
That's true I actually didn't know Ethereum halved their block rewards in januari this year, I just looked it up, and yes that makes a huge difference.
So the only people who are mining this are people with super low electricity costs or people who think Ethereum is going to reach a better price again.
Personally I definitely think Ethereum is undervalued at the moment especially with the rewards that halved but that's just my opinion.