Jobs and Wozniak got rich off Apple, Gates and Balmer off Microsoft. Sinclair was already rich. Tandy, Commodore, Atari, and IBM had hugely popular machines but no "rock stars" single-handedly responsible for their development, and bad business decisions ultimately killed them. Similarly Coleco, which had a great chance to undercut the PC with the Adam and its cheap letter quality printer, but they were too ambitious and by the time they worked out their manufacturing problems the PC had taken root. But the PC killed the rest of the industry by killing itself, making the first clones possible which could run object code generated for other manufacturers' machines, which was Microsoft's second stage to orbit after providing Level II Basic for the TRS-80. It wasn't MIcrosoft's intent, but imagine what today's computer ecosystem would look like if all software was still architecture-specific and there were a dozen or more popular models to choose from.
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Apple and the rest had room to grow because the big names like DEC, Data General, and even IBM were focused on business and saw them as toys. They bought and ate anything that looked like it might compete with them, such as the CP/M office systems which might be a credible threat to minicomputers like the DEC PDP series. That was another gap IBM threaded by being IBM.