Wordpress long predates Google's acquisition of Blogger. In fact, I think hosted Wordpress.com predates the acquisition, too. And even if it didn't, Wordpress already had enough market share and mind share by then thatit didn't have to scrabble to get a foothold against the giant. Plus Google doesn't seem to care much at all about Blogger and hasn't thrown any weight behind it.
It might be because most of the initial bloggers were developers or at least had fair bit of technical knowledge. They wanted more control of both, data and UI.<p>Personally, and I know several people who choose to self host various blogging softwares mainly because they didn't trust 3rd party with their data. Who knows if they will vanish overnight or hold your data hostage.
I feel like one reason I moved from using Blogger to WordPress was because I wanted to use my own domain name as opposed to *.blogspot.com.<p>Not totally sure I'm remember correctly, but I don't believe Blogger offered that at the time (~2005-2006).
wordpress gained huge popularity especially when people were building websites using PHP. Wordpress sites were not just restricted to blogs but it gave you an ability to put up a ecommerce store. it also had plugin marketplace which made it successful.