There's high transaction fees, making small transactions unrealisticIt depends on how quickly you need your transaction to hit the blockchain. As I write this, it takes 117 sats/byte to get into the next block, but if you don't mind waiting for a day, it's 1 sat/byte. 1 sat is one hundred millionth of a bitcoin and is worth $0.00023798. A typical bitcoin transaction is ~250 bytes or $0.059495—6 cents USD.
Here's a tweet about a huge transaction that cost less than $2 [1]. And BTW, the fees are totally transparent; any dashboard or utility can show them to you [2].
It takes quite a while for transactions to be verified. If I'm paying for something on a site I don't want to wait 10 minutes for the payment to be confirmed.
Bitcoin supports fast, cheap (fractions of pennies) off-chain transactions via the Lightning Network, which settles transactions in seconds. You should read the white paper to understand what it's all about [3].
Just to put things in perspective, Lightning Network consists of over 15,000 nodes with over $25 million in liquidity and growing [4].
There's inherent scalability limits with the design of bitcoin, that can't be overcome without forking the network to use a different algorithm
Short answer: there's been several softforks over the years to make Bitcoin more scalable, secure and resilient like SegWit and the upcoming Taproot. There have been several hard forks (Bitcoin Cash being the most noteworthy) and they've all failed [5].
Bitcoin itself seems to have proven it self a very poor as banking system.
It's not trying to be a banking system. The best description is this one from @Travis_Kling:
"Bitcoin is a non-sovereign, hard-capped supply, global, immutable, decentralized digital store of value. It’s an insurance policy against monetary and fiscal policy irresponsibility from central banks and governments globally."
Or is there another reason I'm missing?
In case you haven't noticed, the United States dollar is slowly but surely losing its appeal as the global reserve currency [6]. It's great for transactions but it's been a terrible store of value, having lost 80% of it's buying power the last 100 years. And with the current global pandemic and economic crisis, trillions and trillions of dollars have been printed and there's no end in sight.
People using savings accounts that essentially pay 0% interest are losing money when you take inflation into account. And while CPI is around 2%, in reality real estate, medical care, higher education have inflated by a lot more than 2% a year for most Americans.
Bitcoin can't be inflated or manipulated by governments and central banks. Unlike gold, bitcoin is easy to transport and can easily be converted into a fiat currency in minutes.
And when fiat goes to shit or when government surveillance gets out of hand, bitcoin is the only thing that works. We've seen this already in Greece, Venezuela, Hong Kong and Nigeria.
[1]: https://twitter.com/coinbeastmedia/status/133612299565221888...
[2]: https://bitbo.io
[3]: https://lightning.network
[4]: https://1ml.com
[5]: https://www.investopedia.com/tech/history-bitcoin-hard-forks...
[6]: "The Fraying of the US Global Currency Reserve System"—https://www.lynalden.com/fraying-petrodollar-system/