Serious question, and maybe this is more for r/askengineers, but why was so much failure tolerated to successfully land a rocket upright? Is it feasible to land a rocket on its side?
Take a soda can, glue a lead weight to the bottom. Now scale it up to 15 stories tall. You have roughly the design of the Falcon 9 first stage.
As mentioned, it's designed to take stress in one direction, when empty the vast majority of the weight is in the engines, which will make it want to fall bottom first anyway.
It's not designed as a lifting body, so doing things like attaching wings would require additional reenforcement. For each 5KG you add for landing/recovery equipment/structure, you take 1KG off the maximum payload
The upright landing, landing legs, and grid fins is the most efficient trade-off they've been able to come up with so far.
These rockets are designed to handle longitudinal stress, not transverse stress. Making a rocket able to survive hitting the ground sideways would add way too much weight.
