It failed for similar reason to the ST - didn't keep up with the competition. They should have made 16-bit sound a priority and had it going when ECS came around in 1990. Graphically, AGA should have been more full-featured - at the least a 16 bit colour mode rather than pissing about with the HAM mode and it's inflexibility.
Plus they persisted with the lower specced 68K series chips, realistically by 1992 the 68020 at 14 Mhz should have powered the entry-level machines and 68040 at speeds better than the 25 Mhz of the A4000, although it's worth remembering the 68000 at similar clock speeds had better throughput than probably any x86 up to the 80386SX.
You can apply the same to the ST/TT/Falcon and even the 68K Macs - and the common element again is the CPU. It was almost as if Motorola lost interest in the 68000 by the time they started the joint PPC venture with Apple and IBM. I don't think the 68060 ever saw light of day in a major consumer computer as an OEM component, sure it was available later as an addon by 3rd party manufacturers for Amiga and Falcon but by then it was too late and it was very much a niche/special interest type of purchase.