Well why? Did you see it coming? That is, was it a surprise?
You wonder what would drive a person to do that. It's so pointless. What causes a person to want to erase himself? Is it a backwards kind of grandiosity? "I'll prove how important I am!"
There was an Outer Limits episode called "Don't Open 'Till Doomsday". A one-eyed blob of non-life lives inside a non-space non-time contained in a box, a wedding gift bearing the episode title on the greeting card. People are fascinated by the hum the box emits - and one by one they are drawn to a portal in the side - looking in, they see the non-embodiment of No-thing, and are driven mad.
The thing teleports people into the non-inside of the box, where they cease to exist - no aging, no hunger, no bodily functions - only the eternal probing by the thing - where are my companions? Will you tell me? I am the last component! I am the fundamental frequency! Without me the others are nothing! You must help me find them! We must annihilate existence!
No one - no living human - knows the answer - and finally the thing gets frustrated:
"If I cannot destroy the Universe, then I must un-create myself!"
Not your fault.