why does Sherlock leave the planning of his 'death' so late in the game?

I just finished reading Stranger at the Gate and am full of feeeeeeelings about the transcendental love of Sherlock and John, but seriously for a moment, with my serious face, let's talk about the power of that love, Reichenbach edition.



"If I were assured of your eventual destruction I would,
in the interests of the public, cheerfully accept my own."
Sherlock Holmes, The Final Problem

( Somewhere in there, Sherlock finds a reason to live. And that reason is John Watson. )

When his own token attempt on the roof at convincing John that he's a fraud fails (only this time it was to spare him pain, and then with it's a trick, just a magic trick, Sherlock offers the only truth he can afford), he can't help his small sob because for all his cleverness, it has come to this. John has to watch him die so he would have no questions. Since there will be no body to examine, and witnesses will either be suspiciously silent (Homeless Network) or too easy to trip up (John's bound to have learned a few interrogation tricks, working alongside Sherlock), there has to be no doubt in John's mind. By faking his death, Sherlock does what no one else has managed to do: betray John's trust in him.

All he can do now is hope that John's trust survives his fall.