A PS2 developer may want to do so as a type of copy protection. Somebody today, when implementing a PS2 emulator would want to know about these techniques in order to archive and document these games.
For current systems, sure, a developer might want to make it difficult to run their game in an emulator to deter piracy. There were a handful of Wii games which did that since Dolphin matured while new Wii games were still being released. Nobody is making new commercial PS2 games anymore though, so any anti-emulator trick that wasn't deployed back in the day is never going to matter in practice.
In that era, wasn't emulation so far behind the real hardware that you wouldn't have to worry about emulators until at least 5 years after the console came out?
“Sony had accused Bleem! of engaging in unfair competition by allowing PlayStation BIOSs to be used on a personal computer (…) The Judge had rejected the notion, and issued a protective order to "protect David from Goliath".”
“(As) Bleem! had (…) to deal with defense costs of $1 million per patent”
Fun fact: GBA emulation and homebrew development actually started before the system's release [1]. IIRC, the official devkit was leaked, then someone wrote a summary of the low-level documentation and started circulating that, which (since the CPU had an off-the-shelf ARM core) was enough to start making rudimentary emulators and tech demos.
