Borrowing money from the bank to invest in crypto is essentially betting on which asset would appreciate more, a currency which suffers from inflation and has unlimited supply or an asset with storing value + utility. So yes, it would be weird not to do it.
If he borrows and invests in a bitcoin and the market is a little dumped for a while, how will he repay his loan? We know the potential of Bitcoin which is a market dump but we don't have much tension. But when someone invests that money by borrowing money and the market suddenly dumps that investor will be under a lot of pressure to repay the loan. So in the case of this type of investment, it is necessary to make money which will not be a big loss even if it is lost.
It will really bring a lot of pressure to borrower if what he expected for his investment didnt happened. There's no guarantee to gain and there's no timeframe when you can already take profit since it depends how the market move. As we know it really takes a lot of patience in order to be a gainer in crypto because its not a smooth investment. Hence its not recommended to take a loan to invest especially if you're not certain with the result. Save money as capital to invest is often wise because whatever happens incase you invest it, no one will pressure you because you dont owe money to anyone.