I do not understand either why people use Nicehash. Maybe it is due to alot of people promoting it for the referral income which you can find here: https://www.nicehash.com/referrals
If you have a Youtube channel and get a lot of people using their service through their referral link it will give the promoter a nice reward.

A few months ago when I was actually checking it out I in the end figured out that the buy and hold strategy would be better longterm. Some people might not do that due diligence and end up buying hashpower.