Some people simply make their predictions without any specific reason. Cannot always trust the words of crypto experts which is why I feel that our own research and predictions are what matter at the end of the day. John Mcafee has been making some pretty optimistic predictions about bitcoin in recent times and I do agree with him in some ways. I do feel that bitcoin has the potential to touch 100k in the next 2 years, but 500k is way too optimistic.
Most of us here doesn't always depend on somebody's opinion even those came from the experts, we tend to do our own researches in order for us to answer our own questions, but there are also few that are dependent about the news and from those opinions. It is also true that because of those experts advice there are also some big impact happened and that is why most of the people get interested into listening about predictions.
Yes, some do not even have a basis on their prediction, which is why right now, bitcoin has just become another speculative asset and unless the currency part of it becomes really useful, there is just no way we may experience some pretty huge price and even if we do, it can burst anytime.
However, I would prefer to see bitcoin to be value driven. The prediction by experts though, may end up happening, but we just have to keep our fingers crossed anyway.