They beat Real/QT thanks to marketshare from the bundling deal they'd signed with Microsoft and I really think they thought that would last forever because nobody else would catch up. When the iPhone came out, the public statements made it clear that they didn't seriously expect the no-plugin policy to last or that it'd drive users away – and it certainly never looked like anyone took the ton of problems experienced by Android users seriously enough to take the product out of maintenance mode.

It took years of them being derided as the leading source of browser crashes and exploits before they even started to offer automatic updates in 2012! – and naturally they rolled their own so it didn't work reliably for years.

Similarly, performance was obviously not a priority until it started being heavily mentioned as a reason to prefer the HTML5 stack, at which point they were hopelessly behind and unwilling to invest enough to catch up.

I mentioned my poor support experience because that also fits with the general pattern. The bugs I reported were mostly in the runtime, although the IDE definitely had problems (stability, unreliable debugger, etc.), and all of this was well-known in the community along with the belief that the only way to get attention was if you worked somewhere large enough to buy millions of dollars worth of licenses.

All of that is consistent with my theory that the product management was focused on the short-term and loathe to spend money on anything which wasn't critical, which left them in the unenviable cycle of reacting late to threats from a year or two ago rather than leading anything. If they'd invested in quality during the early 2000s the last decade might have gone very differently.