2) Pixel choices by vector renderers are generally dramatically worse than a human artist's choices. We don't want accuracy, we want perceptual emphasis. Look at NES Mario in your head, then look at the blur you'd get if you took a modern hi-res Mario and vector rendered it at that size. For icons, this can be murder.
3) IE <= 8 is still a pretty significant chunk of your viewers.
4) There's a lot of knowledge built up around how to work with pixel images, especially when sprite sheeting for performance. Much of that knowledge needs to be re-learned for vector. Even when it's a good idea, many developers feel they don't have the time for a knowledge overhaul.
6) For visually complex sites, SVG can still drag on budget and older mobile devices.
7) Older android had SVG turned off in Chrome.
8) It's a lot harder to get vector artists than pixel artists; it's a lot harder for artists to give developers SVG than pixel images.
9) Because it isn't trendy yet.