because bitcoin is a real thing, you can give bitcoin or some portion of it and receive anything physical in return, from paying your check in a restaurant to buying real estate you can do with bitcoin.
but the same thing is not true for altcoins. they are always going to be virtual tokens which only get speculative demand.

because of this, the demand for bitcoin is mostly real and small part speculative. and that demand is rising.
also the supply of bitcoin (unlike most of the altcoins) is small and it also is limited (unlike many altcoins). less supply and rising demand means a huge price and a rising one.

there is currently around 16 million bitcoin available. go and compare this number with the number of coins available for other altcoins. you can use a website like coinmarketcap.com