Factors that lead to Bitcoin price appreciation :
Short term :
1> by the potential fork coming in Nov, if you own a BTC you will own after the fork the same coin on the 2 chains.
2> we are in bubble mode, hence some speculator hold the coin and expect to be driven to 5k or 10k or 100k, who knows...
3> alt-coins, tokens and cryptocurrencies are booming as well, more than half of the investment in altcoins/token is through a first BTC investment, hence liquidity and price of BTC is improved by the alt-coin market.
4> BTC is the natural safe heaven in crypto-currency market. When one alt-coin is falling people will sell it and invest in BTC. This dampens the variations of BTC that is why BTC is so solid and downside is limited.
ETH is the only other coin so far that do have the very same advantages.