Without new hardware, old hardware would eventually die.
When that old hardware dies, it would likely be replaced with a similar design rather than more evolved hardware. This would mean we’d have to develop for longevity. Developing for longevity, could mean that software would flourish. Software flourishing could include malware and inefficient software sold to fight malware. Therefore, it is more secure and efficient to continually evolve operating systems to require new hardware, to reduce longevity and the flourishing of software.