1. When it first came out, it was faster than anything else. It long ago lost that edge, but that got its foot in the door.
2. It came out at a time when Firefox had only just emerged from the ashes of Netscape, and Opera was beginning to feel pretty creaky. It shook up the field.
3. It went to a multi-process architecture early, which made it more stable than competing browsers. The idea that you could use a browser all day and not have it crash out was revolutionary.
3. It offered really good dev tools. Firefox's have caught up, but for a while nothing had anything quite like Chrome.
The data slurping became a concern later. Keep in mind some of what gets filed as "slurping" is optional stuff people actually like, like bookmark sync between systems (which Firefox has added too, now.)