At least in my small European country, I believe you can use a deprecation schedule for software as long you buy it externally, instead of creating it in-house.

The same is true for other creative work/IP. The reasoning being, I believe, that it is hard to appreciate (as in: set a monetary value) for such work. If you buy, you’ve given the open market a chance to work its magic and the price is believed to be closer to something like truth.

This might go a long way towards explaining why company management in Europe often have some kind of mysterious love for vendor supplied software and doesn't see any in-house development as a competitive advantage or worth spending on maintaining.

Code rarely last decades without maintenance and complete rewrites over time - unless you’re the government.

Plenty of enterprises are running decades old code that powers their core business.

I maintain some LOB PHP5 apps, that started as PHP3 - these internal systems are over 10yr old. Just chugging along, producing value for the business. But yeah, pretty rare stuff, and everything I see is small/internal.