Pretty easy:
Sony has a much better reputation worldwide for games/entertainment than Microsoft
Microsoft completely fucked themselves in the reveal, overpriced, underpowered, with an item packaged in that not many wanted.
- Microsoft initially split their attention between TV services that had absolutely no real relevance to anyone outside the US (and not that many cared inside the US), and games. Sony made this mistake with the launch of the PS3, and it didn't help them out of the gate either.
- After the reveal debacle, they didn't help themselves by seemingly reversing, irreversible design decisions
Sony's machine is more powerful
Sony's basically said everything and done everything right, thus far