Sadly I was in at the ground floor, and the first PC I bought was an XT. Prior to that I owned Atari (400, 800, ST etc.)
It's not accurate to ask "Why was the IBM PC so successful". The ARCHITECTURE was popular, not the brand. While we sometimes called
our PC's IBM, we weren't referring to the brand at all, just the architecture. At the time I don't recall anyone caring much about IBM as such.
Right from the off, the architecture encouraged customization, which meant you could buy in now, and upgrade different bits. So standard disc controllers gave way to RLL, monochrome graphics to CGA, EGA, VGA, and Super VGA. Sound went from blips and bleeps to Soundblaster stereo. Monitors got bigger and cheaper. Memory went to 640kb, to a meg, to two meg! And so on. Upgrading was common, and we did it often as the latest graphic cards hit the market etc. As a gamer back then, it was a wonderlnd of excitement.
Better than that - it was the same computer as we used in the office. So its introduction into the home could be easily justified.
On the PC, everything just worked. Meaning, I could buy from any major brand, or build one myself (by far the most common option) and the same software would run on it. If you bought into say, the Atari, then you needed Atari software. The PC was much more open. So the market spoke. We loved going to computer fares, because we knew everything was compatible.
Apple have not changed through the years. They had some good stuff out, but it was sold at a premium. It was out of the price range for most. PC's were CHEAP. Unless you wanted the very latest and greatest, of course.
Oh for the days of a huge TURBO button on the front of the PC.
To be honest I think published history is skewed by reliance on easy monikers. The victors write the history, so it's not always entirely accurate. It's easy to look at the term IBM and derive a view that the company itself was the major force in the success of the platform. But honestly, that's not right. We didn't care anything about IBM - but the platform itself was exciting. Swapping motherboards, modems, video cards was exciting. And this is back in the day when plug and play didn't exist, and you had dip switches everywhere, terminators, interrupts you had to control individually, and BIOS settings that actually did something. Hell, changing out a BIOS was normal too. Great days.
Computing today is much simpler in so many ways.