It's not advisable to build a mining rig right now, GPUS are out of stock in every store in my country and that's not the worst part, I bought my gtx1660 ti for 400$ each and today it's 640$, the fact is people even still don't mind buying this cards at 640$ each, are they stupid? I don't know but getting back ROI should be their most worries, I think it's now nothing but FOMO
Some people are hobbyists and just like being able to mine while never really getting much profit. Also there is the thought that prices will sky for these coins they are mining so they are willing to pay higher prices for these cards. Probably really passing off the gamers out there lol.