The bubble part of it is not their meteoric rise, it's that they can easily be replaced by the next best coin. There is no inherent reason why Bitcoin should be

The bubble part of it is not their meteoric rise, it's that they can easily be replaced by the next best coin. There is no inherent reason why Bitcoin should be more popular than Litecoin as a store of value, except for the fact that it currently is. There will be many hundreds of coins flooding the market. There is no such equivalent in the real (offline) world. You have gold, silver, platinum, etc. - but that's about it. No one is inventing/digging up new types of metals.