Because newbies probably think that investing in cryptocurrency and trading is easy, they rush to take decisions.

Also one of the reasons is that just one click separates them from loosing money - they buy what shows most gains on the exchange right now. I've seen how people sort cryptocurrency trading pair by "descending change" and buy the one that shows most % growth. Their graph is set to 4 hour, or 1 day or even 1 week. They see that altcoin shows a huge growth with probably a little decrease and that suits them perfectly. What they dont know, is that if they switch to 1minute or 5 minute graph, they would see that there are huge volumes of sales and they would understand that they has bought their asset at ATH. And it is not unusual that they go all in with that altcoin.