With digital money like bitcoin it is hard to understand for some but bitcoin certainly has some intrinsic value as the feature of sending any amount of money to anyone in the world alone is so powerful and backed and made possible by the blockchain.
BUT
Bitcoin is very attractive to speculators who drive price up like crazy (noone can argue with me that bitcoin is worth 20k USD in its current state). I think the core technology of bitcoin is worth less than 100 billion USD marketcap for sure. Though I am not saying that the price will not keep rising in fact I think we can go even beyond 100k USD but everything that goes up must come down at the same pace. (Look at some Pump and Dumps or insane bullruns with a correction, they usually happen equally fast).
Bitcoin has significant infatructure built around it but don't forget that there are even altcoins that can do all things that bitcoin can or are even better than it. (Privacy, tx/s, security, waste of energy, etc.)
The Cryptomarket will in my opinion reach a cap of 1-3 trillion USD withing Q2 of 2018.