The inter-terminal train link has been near (or at) the end of its working life for quite some time. A replacement with a fixed walkway with travelators - similar to that installed out to the South Terminal satellite - has been in the Gatwick Airport capital expenditure plans for several years. If they are going ahead with the work in the current environment, you can only conclude that the maintenance costs of keeping the old transit running have now exceeded the cost of replacing it.