Different frameworks and language run-times move at different paces. It's very often the case that projects don't match their product pace and life-cycle to their toolset pace and life-cycle. "Standards" be it ABIs, APIs, data formats or markup languages all have different paces and life-cycles. Then there are the paces and life-cycles of the stacks underneath, the OS, the hardware, networks and data sources.

Then there's the security question. If this is a concern at all, ultimately the system may need to be air-gapped (e.g. like many systems depending on Windows XP are these days) to safely keep it running in lieu of fixes.

Another approach is common in the gaming scene with painstaking work on timing and bug-accurate emulation to keep old software running.

Ultimatley every system has a cost per annum, not a static capital cost. The end game being to maintain the hardware and "firewall" or update the software.