Generally being nice to developers (which tends to get your platforms the largest library of in-gen games) and generally smart pricing are the two qualities that stand out the most to me. Also, at this point their legacy of successes is a factor in its own right.
Those have been the most consistent factors advantaging them, I think. To me. These days the PlayStation brand also stands out for its continued focus on single-player games for adults, which I think there's more demand for out there than the competition realizes. This is the main appeal of the PlayStation brand for me personally these days.
Also they've usually had the right tech for the right time. Timing is important on that stuff! There were 32-bit, CD-based gaming consoles (like the 3DO for example) before the PlayStation, but they didn't take off for reasons of price and inconvenience to developers because the gaming market itself wasn't yet ready to move on from 16-bit. I could go on with examples of what I mean, but the core thing I'm talking about is a pattern of neither falling behind where the market is nor getting ahead of it. Intuiting where the average gamer is and what they can afford at a given juncture.