People believe Bitcoin has value because it's beautifully designed and mining coins takes effort, which gives each coin some kind of intrinsic value in terms of expended energy.
The Dutch believed tulip bulbs had value because the new breeds of tulips were beautifully designed and growing them took effort, which gave each bulb some kind of intrinsic value in terms of expended energy.
What makes a currency robust to bubbles, is it's practical ability to act as a means of transaction. Fiat currencies generally survive bubbles, because they are the only legal tender in some geographical region, making sure that transactions still have to be made with it even after a bubble bursts.
There is no inherit reason for the transaction volume of tulips to stay strong after a burst bubble, because they have no special practical ability. Whereas cryptocurrencies generally have a practical application, like fiat, that makes people want to keep making transactions with them, even after a bubble. The practical application of Bitcoin is its low fees and ease of use for person to person international transfers.
Bitcoins don't really do anything, do they? They're just inert bits. Of course there are computations you can run on them, but the output is not productive.
(Assuming infinite parallel universes, there's bound to be a universe where each bitcoin is the genetic code for an awe-inspiring dragon... But that's not where we live.)
The value in those bits is a cultural intangible: someone you trust tells you that there's a value beyond the practical level. This is like an invisible piece of metadata attached to the seemingly useless information.
It's the same reason why a vintage Gucci bag costs $2000 even though you can get a used leather bag for $5... Or why an Andy Warhol canvas with a dollar sign on it costs $20 million, and one painted by me can't be sold at any price.
I'm not sure what you mean by "Bitcoins don't really do anything". It's a decentralized digital currency with protection against double spending. Isn't that something?
The Dutch believed tulip bulbs had value because the new breeds of tulips were beautifully designed and growing them took effort, which gave each bulb some kind of intrinsic value in terms of expended energy.