It's basically a stand off between Bitcoin enthusiasts and shop owners who need to deal with business operations, taxes, administration and payment processing gear.

I think the gap will decrease over time:

• we see the continued rise of Bitcoin as a value network
• we see a meteoric rise of the capacity on the Lighting Network (LN), with an acceleration this January because of many simple-install-no-own-node-needed mobile wallets appearing
• big improvements on LN expected this year: https://bitcoinexchangeguide.com/bitcoins-lightning-network-sets-up-for-a-major-2019-rollout-while-current-capacity-crosses-540-btc/
• improvements on the Bitcoin protocol (work on further reducing overhead, transaction data size, increasing anonymity)
• increasing doubts among an increasing number of citizens about the long term viability of our current monetary system
• increasing clarity on legality of cryptocurrencies
• increasing capacity of Internet-Everywhere mobile networks (5G coming in the Western World)
• crypto hubs arising (companies like TenX, Crypto.com and Plutus could morph into Paypal like crypto payment processors)
• payment hardware - finally - evolving, making a break with legacy payment networks easier

Infrastructure is being added as we speak. In the end, the gap will be so small that the Big Wave will follows.

For Bitcoin to succeed, fiat only has to fail. Slowly but surely. Drip drip drip.