I can only think of laundering as a reason for overpaying. Whether it be FIAT, or more likely old/tainted coins into new coins either to avoid taxation or muddy the trail.
This is my top 1 most likely scenario, whoever did that was
1- Desperate to get the power, they were way too far from other competitors, they could have paid half what they paid and still got all the hashrate they wanted, but they didn't care
2- Knows enough about mining, their orders were divided between the 4 SHA256 markets ( SHA256 EU, SHA256 USA, SHA256AsicBoost EU, SHA256AsicBoost US)
The second point makes me rule out the possibility of a clueless person playing with a ton of
BTC, and the first point rules out any rational or economical benefit where money laundering is not the sole motive.
Another possibility which doesn't go against any of the above points or I rather call them facts is a software bug, we could easily assume that nicehash is almost entirely controlled by bots, a simple glitch in the software makes the bot do stupid things.