Because newbies probably think that investing in cryptocurrency and trading is easy, they rush to take decisions.
It is very unfortunate that most newbies had come to that end due to their emotions. But I believe that not all newbies think like this, some have also knowledge as they might have some experience in the other form of investments which gives them a reason to survive.
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.
That is certainly hard for them if they just have limited knowledge of the market. I surely seeing that no one will ever succeed in that position. Knowledge is one of the vital things needed in trading, most of the traders are investing this and even to spend a lot of time for this and that is not to wonder how they become successful in the end.