One of the reasons which people may not see is that accepting Bitcoin exposes you to more customers. If I want to buy a product and I see two stores, I'd rather patronize the guy who accepts Bitcoin. Maybe because I don't have enough cash, maybe because I find it credible that he is promoting Bitcoin, but somehow, I patronize that store.
That is if there's more people there that uses bitcoin, what would happen if you're living in a poverty stricken area in your city? That's unlikely that people there are using crypto as a primary currency and they might not even know how it works.
It's a win-win idea. If people in that area don't use crypto, you stand to lose nothing. isn't it?
So the company gain in two ways for accepting bitcoin for payments and if the price of bitcoin goes upward interest are generated also.
So how about the downside? You cant expect only capital gains are in the process. You should also take into account those scenario where bitcoin experience a huge slump. Yes that could also be a factor of going down and totally loss instead of gains. Bitcoin is good type of investment but we must also see its negative impact on some other variables.
Your point is really valid. This is one of the disadvantages of Bitcoin for those who want to use it as a currency. There could be cases where you sell a product and get paid in Bitcoin, but just an hour later, there's a decline in price. This reduces your gain (or can even incurs loss) for the product you sold.