Perception -  With its strong performance over the last 9 years, people are now perceiving it to be digital gold or gold 2.0
Easy transfer of value -  You can transfer funds anwhere in the world without having to wait for banks to process documents
Less cost of transfer - It is cheaper to transfer bitcoins
Inflation - Due to its nature of limited creation, it could be a hedge against inflation

Bitcoin is the most popular , more stable and more reliable cryptocurrency amongst all other cryptocurrencies
So, naturally it is accepted and transacted on every cryptocurrency exchange
It has the largest market cap and is the heavy weight of cryptocurreny overall marketcap
www.coinmarketcap.com
So its easier to obtain and store

There are multiple uses of BITCOIN and other cryptocurrencies
You can buy smalllest of the small things like a coffee in a café to buying houses.
This change has been revolutionary and things will only move ahead from here.
The time is not far where cash would be completely vanished from the world and world will move to digitisation
Digitisation could be bought by bitcoin or other better currency but this will happen for sure.
More and more people have started accepting bitcoins. We will soon have bitcoin ATMs
even loans are now disbursed within seconds using bitcoin and other cryptocurrencies

Criminal activities can increase if the exchanges are not regulated. Governments of all countries are working towards it and we are seeing visible difference now in 2017
Exchanges should follow stricter KYC and AML rules and regulations
Stopping or banning cryptocurrency won't be a solution. It will certainly do more harm than good to the governments.
Countries observing ban on cryptocurrencies will witness cash drain from their country as people have adopted the dawning of cryptocurrencies.

The price of Bitcoin fluctuates
There could be any of these reasons for fluctuations
Economic Factors - Supply / Demand fluctuations
Public Sentiments - Sentimentals attached to ownership of bitcoins
Charts and Trends - Technical analysis trends can have impact on price change
Market News - Banks or reputed individuals and other institutions forming opinions on Bitcoin survival and future
Legal Impositions - Governments posing restricitions or liberaliing use of bitcoin can have a critical impact
Security - Security concerns like hacking into popular exchanges can hurt sentiments in the short run
Mining Difficulty - In the case of proof-of-work blockchains such as Bitcoin, the mining difficulty of a coin can also have a direct relationship with its price.

As more and more people participate in the rally, Bitcoin will keep gaining value.  Bitcoin will continue to create history as sentimentally its viewed as GOLD 2.0