I'm sure a lot of developers upgrade their PCs (they were called workstations at a time) because of material problems - keyboards getting mechanically worse, and laptops can't easily get keyboard fixed, screens getting dead pixels, sockets getting loose, hard-to-find batteries getting less charge, and maybe some electronics degradation.

Another reason is upgrades to software, which maintain general bloat, and which is hard to control; new hardware is easier. That's however is very noticeable.

On top of that, just "better" hardware - say, in a decade one can have significantly better screen, more cores and memory, faster storage; makes easier for large software tasks (video transcoding, big rebuilds of whole toolchains and apps, compute-hungry apps like ML...)