Well, one drawback to the losing party paying legal fees is that it disincentivizes "small" parties from suing larger ones, since they are more likely to lose and less likely to be able to pay.
*I'm quite sure that this solution in Polish legal system was modelled after the German law.
But that's also the big risk: if they're sure they're going to win, spend big to ensure that victory, and then still lose, then they lose far more than they can possibly afford. It's a very risky gamble.
The problem with each side paying their own fees is that there is no such beneficial investment scenario for the party that eventually wins. it's all pure losses and then you win but are not really compensated for the financial cost of defense.