If you lose the wallet which had bitcoins stored in it, you have lost all of your bitcoins in that wallet. You cannot regain it and they are simply lost forever.

In case credit card/debit card stolen, we can call the merchant to cancel the card and request for a new one but in case of Bitcoins, as it is decentralized and no one has control over it , we don’t have any person to call.

Also

Bitcoin prices are very volatile and increases/decreases at a very high pace. Speculators wish to take advantage of it but genuine investors thinks of it as too risky and therefore all the investors does not invest in Bitcoins.