"Isn't really that much" It's alot, because by the third round you have likely already gone for an force in the second round if u got the bomb plant in the first round. So if you lost the force, one player maybe has enough money to buy up an awp without armor and nades (which is really important for the t side), the rest of the team probably has full armor, ak, and some nades.
The thing is that most pro teams have a dedicated awper, an example is GuardiaN. GuardiaN is a dedicated awper because he can win rounds with his awp. My point is that if GuardiaN loses his awp (dies), and his team wins the round no one on his team will be able to buy up an awp on the fourth round because they already fully invested into nades and ak's and full armor, so GuardiaN has to be dropped one ak from one of his teammates because he has to save up for an awp and be able to buy full armor and nades on the fourth round.
So there is a reason why it's so expensive.