I've predominantly worked in two industries, healthcare/public health and insurance where policies terms are measured in decades. The software for both ranges from 20 to 40 years old, and it hasn't been upgraded because to do so poses an existential risk to either the business or, in the case of healthcare, to human life. Upgrades are measured in terms of human generations because of said risk, but I wouldn't call these systems legacy due to not moving beyond java 1.6.

also, the Hyperion Cantos was a great series.