Lots of factors responsible for piracy.
1). Me and others like me - We cracked it, so you could copy it. Only problem with that logic is, if I didn't crack it, someone else would
2). You - You accepted cracked software and didn't buy enough originals. Thats something for your conscience, as no-one forced You to accept cracked software.
3). Commodore - Whilst the Amiga was a great machine, Commodore didn't have a clue how to market it, until the market dictated how it should be pushed (as a games machine). Commodore also fucked up with the AGA series of machines. Sure, the A1200 was a good machine, but, it wasn't all it should have been. When the A1000 was released, it was LIGHT YEARS ahead of everything else. The A1200 however barely caught up with the PC of the day and was quickly beaten in power.
The A1200 wasn't even a huge step up from the A500. Give the A1200 more bitplanes to display more colours.... but give it the same blitter to move all that extra data around?!?!?
16bit sound was STANDARD by the time the A1200 came out, yet we still had to put up with 8bit 4 channel sound. Much as I love the Paula chip, imagine what could have been done with 16 channel 16bit sound?
The DSP that never was, that would have made up for the lack of better blitter and sound processor, the DSP could have made a HUGE difference. Stuff like Doom could have been done easily and competed with PC's of the day without needing processor cards.
4). Cool - Amiga simply wasn't cool anymore. Lots of people that used the Amiga did so because it was cool at the time, but some people soon get bored and want to move onto the next topic/machine, and the A1200 wasn't good enough.
5). Playstation One/PSX - This was the final nail in the coffin, it essentially killed further developer interest in the Amiga, SNES, Megadrive. Developers now had a cheap machine to develop for that could finally compete with the PC and do games that the other three machines simply couldn't do.
5). Programming - Amiga had the best drawn out of it with 68000 ASM, whereas C++ was now the adopted standard. PC versions were written in C++, PS1 was C++, Saturn was C++. Sure there were some optimisations in ASM for the individual machines, but the effort to translate C++ to ASM to get the best out of the Amiga, well it was more effort than developers were prepared to do.
TFX proves that quite conclusively, even on 060 it was dog slow, and that helped make the decision to abandon the Amiga.
Lots of factors, not one in particular is to blame, but all contribute.