Some already do via bitpay I believe. The thing is bitcoin took a big reputation hit because of the spam attacks that raised the transaction fees temporarily. Lately the fees are way lower but the damage is done already. People think high fees can return anytime, that’s why they hesitate to use btc as a currency. That’s why businesses don’t bother to invest in the infrastructure. It is because bitcoin transaction fees are not reliable. Yes they are cheap now but nobody knows what will happen tomorrow. Businesses would rather invest in credit card payment systems and customers also follow the same path because it is way more convenient. The situation might change for the good in the future but it is what it is now.