The financial answer to Chinese technology sharing

Why is China more willing to share technology and expertise with Pakistan than with North Korea, despite North Korea being its treaty ally?

The only explanation offered is that Pakistan can pay its bills while North Korea cannot.

The explanation is bluntly financial: Pakistan can pay for cooperation and North Korea cannot. The exchange does not address alliance politics, security concerns, or any specific technology transfer. Its conclusion is economic and deliberately narrow. Other possible reasons remain outside this brief answer.