The dot-com period was just the latest example of what happens when a new technology is widely adopted. Automobiles famously went through a similar period early last century. Many new entrants crowd into the field, there's a free-for-all as everyone tries to make the killer app, then through a weird alchemy of vision, execution, and luck a few brands eventually buy up or force into bankruptcy enough competitors to dominate the field. In recent history at least, explosion and consolidation of new players is the norm when a new technology is introduced.
As to your second question - which I would rephrase as 'why would this technology be widely adopted?' I would say, if the role of a trusted third party can be automated, it will be because nature abhors inefficiency. And trusted third parties aren't a niche field - not just banks but also a large part of any civil service can now replace humans with algorithms. That's a lot of disruption.
