I would gladly make a purchase of many hardware wallets using Bitcoin and sell some off them off later. Btw it baffles me sometimes to find a legitimate online shop selling crypto related items and yet there is no payment option in form of crypto. All use see are PayPal and other bank transfer payment options
I guess , they are afraid of volatility. Bitcoin swinging 10% to downside will hamper their profit. (you can say it can go up 10% too but when we start business we like to have well defined sustainability and profit model) i.e one of reason I guess.
Second, we are all used to current system, it will take time to adopt or start a new system.
You are right. For a merchant, it needs a stable business model that can predict his costs and benefits, and the huge volatility of Bitcoin will make its budget meaningless, and its profitability will depend more on Bitcoin's rise than on selling goods to earn a difference. This is a situation that every merchant is not willing to see.
If I am a merchant, I will accept crypto payments, but only choose those that are stable.