its the same with art its just some paint on a canvas and it can be worth alot of money, or it can be worthless, same with everything realy things are worth what people are willing to pay for them.
Many things as such we have given value to them because of our own reasons and art is definitely one of them and that is only applicable to those who collect and trade in art because of historical value. These are traditions like gold collecting and they do give that person and their prodigy an asset to secure over the years.
Bitcoin can be thought as an asset albeit a risky one because of market fluctuations but same is for other precious metals and stocks. We do think of speculative market as gambling but people see the value in the support behind bitcoin and its ideology.