Right, there was a golden age of interesting DVCSs around then - Darcs (2003), Monotone (2003), Bazaar (2005), Git (2005), Mercurial (2005), Fossil (2006).
It's not just the big name -- Linus learned from the mistakes of the older DVCSs. I also used to use Arch a bit. Git was a vast improvement (eg. it didn't force you to use long ugly branch names).
It has a much cleaner interface, easier to use, better formalism, code signing is built-in and required rather than tacked-on and optional, and insanely good documentation (I still sometimes recommend people to read the monotone docs as an introduction to git/DVCS).
It was also basically finished and stable when the BitKeeper drama happened. It was one of the few alternatives Linus looked at and publicly evaluated before writing git. But unfortunately, its performance was pretty poor for a project the size of Linux at the time, and a combination of human failings + the well architected abstractions which hid the underlying monotone data structures convinced Linus that it was less effort to write git than to fix monotone.
In a literal sense that was true since git was basically written in a weekend.. but more than a decade on we're still basically stuck with all the design short-cuts and short-falls of a weekend project. The world would be a better place if we used monotone instead :(
Edit: these days I'm more a fan of the formalism of darcs, and really looking forward to a stable pijul. But there is a soft spot in my heart for monotone, and more than once I've considered forking it to modernize with compact elliptic curve crypto instead of RSA and a faster non-relational database or filesystem backend instead of SQLite.