Stress relief. Thermal / moisture expansion of the PC board (and this looks like shoddy phenolic paper) bends the leads a tiny bit and the bending forces go through the component. By making the leads longer, they are less stiff and require less force to accommodate, so less drift due to this.

It was a relatively common method in precision electronics.

There could be other reasons as well, e.g. if these were ceramic capacitors they might do that to avoid cracking issues. (Because ceramic capacitors drift a lot by themselves, a drift/precision explanation does not make sense)