Why would I want to keep BTC in my investment portfolio? That's most hyped and quite overvalued coin I'd say.
There are other more technologically advanced coins. Is it because of "digital gold" and store of value properties?
This does not make the bitcoin successful, because bitcoin is the first altcoin as well as accepted by the community as a common currency for exchanging other altcoins. And it is the investor and investor most interested and invested.