Bitcoin is not completely implemented in every country and due to very low transaction fee many people are using for illegal activities, The price of bitcoin is also not stable.

I agree that bitcoin is not totally implemented and accepted in all countries. There are only few countries who are already using bitcoin in their transactions. And not all people or government are willing to use bitcoin, they have so many questions that needed to be answered. And also bitcoin can be hacked easily by those people who know how to hack because it is sensitive and can easily be hacked.

I think one of the biggest disadvantages of bitcoin is the volatility of its price. 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.

I don't think something as the disadvantages of bitcoin or blockchain technology. People without experiencing the goodness indicate it as an failed technology but in reality everyone are in much temptation to implement blockchain technology into their working sectors. It is true that future technology development will grow with blockchain as the base.

there are number of things to think about.

The fact that nobody can control it.
The instability of the price.
The inability to charge crazy bank like fees for using it.
The fact that it is almost anonymous.
It wasn't created by 'them'.
Still a new technology, unproven.
Has received a lot of negativity, bad press & illegal happenings.

These are just a few that come to mind right now.