Legacy technologies (such as mainframes) have multiple complex components that depend on each other. These are extensive proprietary and costly servers that are not readily available if someone wants to develop skills on their own. It is challenging to retain application-development resources, and even more challenging to hire people with hands-on experience in old technology and operating systems.
Often, legacy systems are two or more decades older, and most of the workforce with those skills has retired. Also, these systems don't have the proper documentation to keep up the record of years of work. There are chances of significant knowledge loss as an older workforce rotates with a newer workforce. A lack of knowledge makes it riskier to change the system due to unknown dependencies. Any small feature requests are challenging to accommodate, due to system complexity and skill-set shortages.
New cutting-edge technologies such as big data, machine...