The cost of a Pentium III and the electricity to run it might be much, much less that the cost of labor to move one application over to a Raspberry Pi.
Then the cost of debugging the application on a Pi 4 might be more than the value of the company trying to run it.
You were sold a silly idea: that the reason software isn't portable has to do with work and resources. That's simply not true in a vast majority of instances. Companies intentionally lock software to certain platforms for sales reasons much, much more often than for technical reasons.
OTOH, Windows isn't portable, so if you want to run old Windows software, you don't move it - you emulate it.
Then the cost of debugging the application on a Pi 4 might be more than the value of the company trying to run it.