So EVERY believer goes through Purgatory then? You just said some will not because they are perfectly cleansed and will go straight to heaven (I.e.., Saints). My point is that this passage is not talking about Purgatory but the Judgment Seat of Christ of which ALL believers will go before to receive rewards for the works they have done or the loss of reward due to the quality of their works.
Seems to me, you are expecting this passage to give you a complete handbook of routes to Heaven. Every believer (one built on the foundation of Christ) goes through individual judgment. If his soul is clean, nothing to burn off it and he does not “suffer loss”. If his soul is not clean, then he needs to be rid of impurities.
The passage does not concern unbelievers and generally those who cannot be purified, but we know that they are judged as well and sent to hell from, for example, Romans 2:6-8 or Matthew 25:31-46.