Isn't Lightning a 3rd party app?
And is not Steemit a 3rd party app? Steemit or Lightning Network are overlays for cryptocurrencies. Lightning allows scaling, and Steemit communicates with blockchain.
Bitcoin is accepted in very few places, so to utilize it, one needs to go through and exchange and or a bank.
Sure, but it still has a much better developed store architecture compared to Steem. As I have 2 commercial projects on Steem (shop and market), I will tell you where the problem - In terrible decisions Steemit Inc. and ned.