What is the purpose of the PCB jumpers in the attached image
It is a super-cheap single-sided paper-based phenolic PCB (probably punched rather than drilled holes, judging by how large they are). 

It's to save money compared to a fancy double-sided PCB with drilled plated-through holes. 

The cost savings will easily pay for the salary of the engineers, and if you don't do it, they will save the cost of your salary by shunting  you out onto the mean streets of Tokyo or Taipei and find someone who will.  

Another issue from that time is that it's easier to get consistent quality of production with single-sided PCBs. The chemical process of making plated-through holes is sensitive to contamination and easy to get wrong. It only seems straightforward now that many low-cost fabs have mastered the process control. In the 1990s it was not uncommon to see bad (intermittently bad on 100%-tested!) plated-through holes and hair shorts.