Saving weapons and nades in CSGO is a very intricate part of the entire complexity of the game. However more often than note the confidence ( sometimes overconfidence ) of the professional players and their belief in their game means that they end up not saving their weapons. They might end up getting a few more kills, but they put their team at a severe disadvantage in term sof the financial situation
Thoorin video explains the same and in detail. Of Course it is easy to criticise the professional players from a third persons view, but logically it sometimes does not make sense to go for these kills even if you know that your death will put your team at a disadvantage.