As legacy systems have been all set up and working for decades, they may look less expensive. But over time, the total cost of ownership turns out to be higher, as support and updates for older systems are usually more costly. Often, those updates are not available out of the box, and lots of manual workarounds are required to maintain the system. Most legacy systems are not very automation-friendly, resulting in more human effort.
Legacy systems mostly have a large chunk of proprietary software, which results in significantly higher license fees. In addition to that, older software no longer receives support from providers, and buying additional support out of the life cycle could be very costly. On the other hand, modern systems mostly adopt open source technologies that drive the cost down. The operational outage from a legacy system can take more time to recover from and drives up operational expenses. People with the skill set to maintain legacy...