[bostik]

> deliberately destroy old notes and issue new ones with different images to replace them

Big part of the reason for this appears to be security. Many years ago a high-ranking official from Finnish central bank told in an interview that bank notes need to be redesigned approximately once per decade. Reason is that it takes about that long for the materials and printing technology to get commoditised enough for criminal enterprises to be able to start manufacturing "high-grade" forgeries at any real scale.

Every generation of bank notes employs a whole bunch of newly developed technologies and tricks that make the notes themselves distinctive, as well as incredibly difficult[ß] to forge.

ß: Some of it is down to tightly locked down and guarded speciality supply chains. Some is due to advances in microprinting and ilk. If you had unlimited resources, you could arrange to have the necessary equipment, supplies, staff and materials to print your own forged money. It'd just be slow, low-yield and very expensive.