If the people really don't want to share their keys it's their right but those coins will be dead as well since it can't be access so if you really don't want to share your keys maybe you could make a riddle and ask your family to share it online or to them that if you die, they would try to crack the code and if anyone gets it then the coins will be theirs.

There's no other solution if the person really don't want to share their keys even if you try to force crack their wallet it's impossible.

Worry no more, you'll just need to read these previous topics on how you can create a strategic plan after your death.

What happens to my bitcoin if I die today?
Inheriting Bitcoin
Bitcoin Inheritance Planning

Interesting topics.
But it's worth thinking that we may end up locking up huge amount of bitcoins like this. What if everyone option out not to share the keys with anyone else?

May be there could be one option. Everyone should right down the keys in their Power Will and submit the same with their lawyers. I think that way they can protect the privacy of the keys legally and will not be afraid of loosing them ever. Whether we die or not we will know very well they will be used somehow.

When a person dies he won't gonna need to worry about what he left in this world let alone some crypto assets he left in his hard wallet. That's why if we really want to share our blessings, we need to set up who will inherit them after we perish. There is lots of basic information on how we can teach the person we want to take everything we have after we left this world and they can be as easy to explain to them. But the most common is teaching them the basic today so when you are not here anymore, they can get everything you have and spend it the way you want it to.

If you do not tell your password or keys to anyone, your coins will remain in your wallet and buried for a long time until someone can know the password.
There is no solution for that if you do not tell your password, what you have will not be accessed by your family.
If you want to give your coins as a legacy, you should tell them the password or at least, you can try to make a testament for your family and give it to the right person you trust.
If something wrong with you, that person must tell your family all about what you did in crypto and give them the information that they needed to access the wallet.

Lets suppose 50% of the people share their keys so that in event of their death their coins could be benefit to their family. The rest 50% don't share keys and those bitcoins could not be used after their death. This means that supply of bitcoin will keep on decreasing as many of those bitcoins will be practically not usable.

Or a much better one would probably teaching them right now about bitcoin and then have your important information locked in a safe place and then let them do what they want to do with it, you are already dead so it's pretty foolish to think about it.

It's a good idea, but I don't like the way it is set up. Having a centralized service store your encrypted message, which will presumably be your seed phrase, and handing out the decryption key to your family and friends is the wrong way to do things. You are still trusting the service in question to properly encrypt your message, to securely store that message, and not to have the unencrypted message stolen by other malware or attacks on your computer. Very few people will choose a decryption key with 128 bits of security, meaning the security of your seed phrase will be reduced the whatever the security of your password is.

Much better to give your family and friends your encrypted seed phrase, and have a third party service store and email out the decryption key.

Again, you are now trusting a third party with complete access to your coins if you hand over your keys or seed phrase in plain text. Better to give your family members your encrypted seed phrase and store the decryption key with your lawyers.

You're certain? There's no way that someone might glance at it in a filling cabinet somewhere? Or that it might get scanned and uploaded to server, and someone might take a look at it? Or when you are updating your Will that an intern somewhere might be handed the old copy to shred? I would never hand over your seed phrase or keys in plain text to a third party, regardless of how reputable they are or what processes you think are in place. Things go wrong and things slip through the cracks all the time.

What I have outlined above - encrypted seed phrase with heirs, decryption key with lawyers or other trusted third party. Alternatively, a time locked transaction. I set up a transaction moving all the coins in my cold storage to my heir's address, but timelock it so it cannot be broadcast before block 741,000 - roughly one year from now. I hand this transaction over to my heir. Once we hit block 741,000, they can broadcast it and claim all my coins. If I am still alive, then at some point prior to block 741,000 I move all the coins in my cold storage to a new address, thereby invalidating the timelocked transaction they are holding, and provide them with a new timelocked transaction, this one unable to be spent prior to block 795,000, roughly another year on. Timelock can also be performed with Unix time if you want to be exact and don't want to depend on the variability of the average block time.

I have my wallet keys saved on my hard drive and my son and wife have the password to my hard drive but are only permitted to use it on my instructions or when am not accessible to use it. This has helped me to secure my coins, I can't afford to risk my digital assets so I let my family have access to my keys and passwords.