Self-custody has always been a bad idea for the simple reason that most people are not security experts, they do not live their lives in a high security context, and most importantly they do not want to. What good is having more money when that money diminishes your lifestyle? Living in constant fear that you may accidentally lose your life savings, or that you may be beaten or killed because of that savings is no way to live. If you have to wake up every morning and check to make sure your self-custody product(s) are still secure, your life is diminished.
If someone loses bitcoins in self-custody due to their own weakness or ignorance, the custody is not responsible, but the person who was unable to use the facility is. Moreover, a single wallet failure will never be considered a threat to all wallets. It is certainly wrong to say that if one wallet is hacked, the entire self-custody system will be hacked.
Since Bitcoin is the most volatile, insurance companies will not be interested in taking insurance against it, and even if they do take insurance, there will be many conditions that will definitely be difficult for the investor to accept. If the insurance companies refuse to pay their insurance money as conditions due to hacking or bankruptcy of the exchange, then there is no logic in taking that insurance.
If you have to take the help of a third party to use Bitcoin, there is no need to use Bitcoin. Of course, I think there is no alternative to self-custody. If you want to use and hold Bitcoin as you wish without relying on third party, there is definitely no alternative to self-custody.
Those who want to hold Bitcoin for the long term, if they use a hardware wallet and store their seed phrase and keep private key properly in offline, then it is definitely the safest for them to hold Bitcoin. Since the original purpose of Bitcoin's creation was to rely on its decentralized system where everyone will have the benefit of money transactions without the help of any third party. If someone does not use self-custody, then he will be deprived of the benefits of Bitcoin's decentralized system.