The body / fore limb / hind limb / tail proportions and the supposed posture of the T. Rex are very suspiciously similar to those of hopping animals like kangaroos or hopping mice.
The hopping style of movement tends to evolve in land animals that have to efficiently travel relatively large distances between spots where food and/or water can be found, which is why it's most prevalent in arid climates.
The T. Rex was a scavenger specialised in feeding on corpses of other large dinosaurs, which are scarce and usually far in-between by nature.
thump. thump. thump. thump. THUMP. THUMP. THUMP.
(Yeah, yeah, I know that the structure of its leg bones doesn't really fit that and the paleobiologists analysing T. Rex remains wouldn't have missed the required massive tendon attachment points and other features required for efficiently absorbing landing shocks and transforming them into springy jumps. But it's too fun of a mental image to pass up.)
