Haha, its strange to make a statement about business model making no sense because they actually
make money from it, at least for now. This, is only 1 billion dollar industry for now, but I believe its going to expend much more in the next year or so.
There are lots of competition with all that DEFI projects...
Of course, there are bad players, as in any industry, not just
crypto.
On other hand, taking a loan instead of selling your crypto is a non tax event, and in reality and compared to 90% average gain of
bitcoin for the past 10 years, is something worth considering, this is one reason.
Another reason, as you mentioned, they believe that price will go up at some point, so they prefer to pay % and keep their holdings. This way or another, this industry came from nowhere and if you look at defipilse website it shows you how much collateral has been deposited in those defi project (by the way, nexo is a custodial service)
And, of course, this industry has holes,as anything new....