Amigas ended with AGA, the other systems are alternative systems that users insist on holding back with AOS derivatives and dated software.
I'm amused by this statement, if your "amiga" is only the old hardware then you've had the option to run netbsd, linux, minix, or whatever experimental open source with whatever features you've wanted to port to it for all these years, or to just ignore it completely like the game or demo developers who just followed the Amiga hardware reference manual to make a bootable floppy and ignored the whole multi-tasking Amiga operating system user experience for their area of interest. One wonders what "m a g i c" you think could/should be developed now for m68k aga or ecs machines?
Its the user experience, that other non-amiga-like OSes (even with their faster than m68k-CPUs, memory protection, multi-core, hardware accelerated 3D, office and adobe software support) commercial or open sourced, which has driven people to pursue the "AOS derivatives" for an alternative that seems more Amiga-like to them. Its the lack of funding for full time development staffs, that has held back development of these alternatives, not the demanding an Amiga experience like one is familiar with.