Inkscape could have had the world if they just copied Adobe Illustrator, but instead they came up with their own unfamiliar UI. I'm not saying their UI is worse that Illustrator (although I feel that way personally), but it's not better enough to justify the learning curve. I have to imagine Inkscape contributors were smart enough to realize this, so I guess they were afraid of getting sued. Same goes for Gimp/Photoshop.