Most of the reasons for the Amiga's death have been posted already, but I abondonned it twice, for different reasons.
In 1995 I bought my first PC which effectively retired my A1200. The reason then was that all my Amiga owning friends had left the platform and got PC's. As the only remaining Amiga user I felt increasingly behind the times. At work it was all PC's, I was in support looking after them! Pentiums had arrived and the cost of upgrading the A1200 was too high when I could get a brand new PC on interest free credit!
A couple of years later, on my second or third clone by now, my dual boot 95/NT4 PC had once again ####ed itself up and was refusing to boot. I made an on the spot decission to return to the Amiga. I had plenty of cash at the time and was sick to death of the comparable instabillity of the PC. I remember thinking at the time that I must have reinstalled windows on personal and work machines hundreds of times in my few years to rectify fault yet could not recall one single incident where I'd had to reinstall AmigaOS.
The VERY NEXT DAY I phoned Eyetech, ordered a brand new A1200T with dual 060/PPC240MHz+SCSI, 128MB RAM (I think) VGA adapter so I could use my monitor, 3.1 roms and the new OS etc, all the bells & whistles. I'd kept buying Amiga magazines and knew what hardware was available so I ordered it all

Cost me well clear of £1k including SCSI drive, SCSI CDBurner & SCSI ZIP Drive.
When it arrived I formatted the NT disk, threw the PC into the corner and slotted in the Amiga and installed the OS. I was home again. I was so pleased to be back where I belonged, on the Amiga, and just about the fastest Amiga you could buy. Particularly so once I got my BVision some months later.
I had the money now to spend on the hardware and keep up with PCs. Last year I abandonned the Amiga again. This time it was for reasons I just could not see improving:-
1. Constant promises by the idiots at Amiga and in the Amiga press about new hardware, new OS. A long time after I had realised, thanks to the BoXeR, that nothing could be trusted and nothing should be expected.
2. The internet. YAM was great. AmIRC was, and still is, THE best IRC client. When it came to browsers, my god did the Amiga browsers suck. They were good efforts, all credit to the developers, but the PC was moving so fast that the Amiga was rapidly becoming hopeless. Plenty of promises about Opera ports, mozilla source, all broken in the end. I eventually installed MacOS and Netscape which kept me going for a while.
3. My Amiga didn't power on one day, it was a minor problem that I fixed quickly but it scared me. I realised that with Phase5 long dead and quoted fixtimes for their boards measured in several months that if my Amiga were to die on me I would be completely and totally screwed. With only Eyetech and Power dealing Amiga and everyone else abroad and slow, me knowing no other Amiga users, moving into web development professionally and having to rely on Amiga browsers and once again starting to lag behind the world on the hardware front, only this time with no Phase5 around to save the day, well, all I had to cling to were yet more promises of a distant AmigaOne and OS4. I sold up. I dn't regret it, I regret having no real choice.
With the profits from the Sale I built an Athlon PC and purchased a few small upgrades for my spare A1200 so that I still had a decent enough Amiga. It's sat here with me, it doesn't get much use these days but it is always there when I need it.
I look at sites like this every few months to see if there are any new developments. I was surprised and pleased to see the AmigaOne actually arrive but to me it just looks like a very slow and expensive way to run Linux :/
If it were possible for me to dive back into the Amiga with decent, modern hardware, I'd be there in a second. But that will never happen. Certainly not now the latest Amiga Inc seem to have proved as useless as all previous incarnations.
I don't even know if they still exist, their site is down, perhaps they're bankrupt.
Selling the Amiga that second time was painful. I love the Amiga, it's a very special machine to me that changed the course of my life. I loved being part of the rebellion against Micro$oft. I loved being different. There's not much I wouldn't do to roll back the IT clock to the days when I, and the rest of the Amiga community, could sit back, smug in the knowledge that *we* were the enlightened ones and our machines were the most amazing computers ever built.