Fot now most of the store accepting bitcoin because it is popular and it is the main coin of all coins in cryptocurrency.
Altcoins will also popular but not just like bitcoin but you can see for sure a lot of store also accepting altcoins like ethereum the moat potential coin for now. But bitcoin is different because even it did not popular because they have pizza store who accepting bitcoin and fot sure the guy who use his bitcoin are losing more opportunity.Let's wait for the altcoins to grow more maybe it is not their time but surely in the future will the altcoins have many uses but for now they use usually in gambling and for the others.