Just the on-ramp cost is expensive. The CPU intensive plotting. But after that the HDDs don't draw much power. So there is a huge difference plotting once and then farming vs. GPU mining, which continuously draws a lot of power.
Drawing a lot of power doesn't matter if one is mining a profitable coin using the GPUs. The problem with Chia is the coin price has plummeted sharply over the past month, and we don't know how far it's going to drop. I am sure there are people who spent a lot of money buying the HDD's when the profitability was promising, but are now stuck because of the current situation. I hope the risking pay off after some time.