Let see something, what was barely mentioned here: HW flaws .
Actually, there is not much of them, but in my opinion there is one huge flaw: lack of CPU bus + some other things expansion bus/connector, compatible across many models .
Above sounds pretty awkward, but I needed exact formulation of what it should do . Explanation below:
Atari was on that no need for it - there is cartridge port, there is DMA, (ACSI port) . Yes, that was good for some things like laser printer in that time. Cartridge port was used for diverse things, like video digitizer - not because port was really good for it, but because there was no better one ! I made EPROM programmer for ST in 1987, for cartridge port, and that needed some tricks to work - because cartridge port does not support write, only read. Short sighting design, that's it ...
What about users who want to expand RAM, update TOS ? Those 2 things are elementary - I know it for sure, since I made those upgrades for many Atari users. We could talk here about some other upgrades like video cards and like, but let say that it was told that Atari ST is closed system. But should it be closed for RAM, ROM updates ? I think that this mistake costed Atari at least million buyers.
Because this trivial upgrades people needed bringing computer to service and pay all work about opening machine, soldering there, adding PCBs ...
What should be done, and what it would cost ? First to say that I did not discover hot water. Such expansions were present in many micros of that time. So, on expansion slot should be CPU bus, 5V power, some interrupt signals (for disks) and because ST has special RAM circuit DRAM lines and signals. Optionally even some video signals. And all it with added extra lines for future models (reserved pins) .
With it, people could add in minutes RAM expansions, new TOS versions. And other things - like EPROM programmer without tricky write.
The price of such port ? Including all, max some 20 bucks . The price of not putting it in design, sold machines: Hundreds of millions lost because lower sales.
And that they knew that expansion slot is necessary proof is Mega ST - well, it's slot includes not all signals I mentioned. RAM and ROM upgrade was still on services. Or very skilled users + hours of work.
And then - TT, Mega STE - they went on VME bus ... No comment. Falcon - again new expansion bus. That's just not good way to keep people at companies products. Amiga did it better. PC did it better. You always can use little older cards in some PC - like PCI ones in latest mainboards, where there are mostly later PCI-E slots . Because today football World Championship is starting, I will say:
Atari did not get goal, they gave self auto-goal