Curious why does it need to wait so long to reorient? I thought it was going to crash and in last few hundred feet, it flipped! Can it orient straight - way up in the air like Falcon boosters?

Reorienting requires the use of main engines. You want to relight them only once, to ensure that the header tanks and the "downcomer" remain full. Additionally you want to burn off as much speed as possible with the bellyflop, so flipping vertical as late as possible. All combined this means combining the landing burn with the flip is best, as close to landing as possible.

It has a cute nickname, “Suicide Burn”.

Why is it efficient? [https://www.reddit.com/r/KerbalSpaceProgram/comments/2z534g/...]

Guessing we won't be using constant altitude landings in real life?

It actuallyoriented perfectly, but due to the flip, fuel pressure was lost leading an oxygen rich exhaust eating away the engine (becoming what's known as engine rich exhaust) before it was able to complete the landing burn. They should just have to fix the fuel pressure problem to have a complete success.

I'm very dumb so I'm asking: is "engine rich exhaust" a real term?

What do you mean by "real term"?

Real rocket science teams really use phrases like this, including this one. Is it a joke? Yeah, kind of. Is it what they would say if they had no sense of humour? No, probably not. Is it still a thing the experts actually say to actually talk about what's going on? Yeah, it is.

a few more examples:

"Rapid Unscheduled Disassembly" : explosive destruction of the rocket

"Lithobraking" : it's like aerobraking, but with less aero and more litho