Because there aren’t enough Inception trailer mashups out there (there really aren’t — a year later and this is a meme that keeps on giving). Plus, Speed Racer works so much better as a fever dream, dontcha think?
What’s fascinating is how well the two different trailers matched up. I had to do very little actual editing to make the mashup click. If nothing else, it shows that the people who make trailers for movies really have their craft down to a solid formula these days.