-snip-I don't know why OP is saying one shouldn't invest early,when it is the early investors that have benefitted more from bitcoin because they bought bitcoin when the price was very cheap.
I guess OP is referring to the newbies who invest in Bitcoin without understanding the Bitcoin firstly. There are many newbies who invest in Bitcoin because they follow the hype only. They probably hear that people can be rich instantly by investing in Bitcoin, and they think it is an easy matter. Even worse, they don't know the risks of Bitcoin investment. They also never learn how to deal with the risks.
Early investors bought Bitcoin when the price was very cheap. So they don't use big money to buy the Bitcoin. They won't regret it even if Bitcoin have no value in the future because it is a small money only. It is different when we invest in Bitcoin now, the price is already quite expensive. So, people will regret it if they lose a big amount of money.
There are some people who loves and believes in something that they haven't tried but because they understand what might happen tomorrow, they will take advantage of the belief and invest to hive it a trial.
People want to speculate on something they never experienced because they know well about it. Although it may be the first time they try it, but they already learn it deeply. I am sure no people who purely want to speculate on something that they really don't understand it. No one wants to waste his/her money, especially if it is a big amount of money.
This was how some early investors gave bitcoin a trial because they love the privacy and financial freedom attached to it and not because they think that the price will soar high to this extend.
For the early investors in Bitcoin, they only know it will be a digital currency in the future. It was actually described by the Satoshi on the whitepaper. But since the price keep increasing and there are more and more people want to buy it, people view it as a future asset as well. I assume most people aren't involved in Bitcoin because of loving the privacy or financial freedom, but it is about the potential of the future of Bitcoin.