Because history has shown us that you cannot scale a single protocol to 8 billion people on the base layer. Would bet a good amount of satoshis that some shitcoin called kaspa is not going to magicall...
What would be the point in custodial bitcoin? One of the main reasons bitcoin was invented is to have a private, decentralised, non custodial digital currency that doesn't depend on centralised companies like visa/paypal. WHy would anyone buy bitcoin and use coinbase instead of just using paypal, other than for asset speculation purposes?
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