Merchants don't adopt Bitcoin because their clients don't use it. Clients don't adopt it because merchants don't support it, and people want to have a payment method that can be used anywhere they go. How can this vicious circle be broken? Who will make the first move?
And by adopt I mean adopt for payments, not hodl it as an investment.
That's not entirely true.
Most of the times :
The government doesn't really comply with these terms. The merchants and the clients might not even have a hand in this.
When you see the price of Bitcoins rising, you won't use it as a payment method, why would you? Generally you would actually use it as an investment and hold it for a long period of time. That would decrease their demand as well which would prompt the sellers to choose not to engage in cryptocurrencies like bitcoins.
I do think that, merchants and clients would only accept Bitcoins when it would be more beneficial to use it for transactions for examples :
1. For international transactions
2. Transactions needing third parties
For the regular basis I do think that it would be more advisable for the clients to hold their bitcoins since right now it's more profitable. When the price is stable, it might be a good idea tho. It's a lot about situations as well.