It's mostly a matter of regulation, but there's bound to be a lot of other things that would cause it to not be used. I don't think traders really want to use bitcoin as a means of payment, that just doesn't seem right considering they just want to profit from the trades they make. Trader are the smallest in terms of adoption, they do not use bitcoin as a means of payment although in some cases some of them can use it for certain services.
The risk of volatility is the most talked about thing when one talks about the adoption of bitcoin as a means of payment. I can justify that, and by far it has been the most influencing factor for bitcoin adopters out there even in countries that have legalized bitcoin as a means of payment like El Salvador.
Having volatility issues is one thing that doubt others to use bitcoin as a payment method because it’s price keeps on changing and is never fixed. And to think that bitcoin is much better when used as an investment rather than spending it like fiat, then it’s not surprising that most traders would want to hold and trade it later since they will surely benefit huge profits from it.