Software has incredible inertia compared to hardware.
It is effectively trivial to buy millions of dollars of hardware to upgrade your stuff when compared with paying for existing software to be rewritten for a new platform.
This is a very SWE-centric perspective. The very names of software/hardwsre would imply the exact opposite.
Funnily enough I worked at a company with a codebase written in the 1980s - no idea what it originally ran on but someone decided in the mid 2000s to update it to run on modern hardware. Unfortunately they chose Itanium... so 20 years later they're paying lots of money for Itanium hardware.