because. we already got the Elite Trio of Daredevil (Matt, Foggy, and Karen) confirmed to be Snap survivors, plus these footnotes from Daisy Johnson/Quake's (Agents of SHIELD) and Dinah Madani's (The Punisher) Wiki pages respectively forcing the characters into Snap survivors:

not to mention the contentious placing timeline-wise (particularly for The Punisher season 2 and Jessica Jones season 3) because -TV and -Studios were two different production entities at the time, and despite Jeph Loeb saying in 2018 that every show (as of 2018) happened pre-Snap, it still leaves a few outliers.

Note: I grew up kinda sheltered/primarily without internet access, so I haven’t discovered fandoms and fanfic until college. Never wrote any officially before. But I think this concept counts as the beginnings of one.

Background

“When half the human population vanished in a snap, most results were bad. There was some good in it, as in all tragedy; some people began to care more about others, taking in strangers to replace their own losses or giving aid to what was left of humanity [this will be relevant later to how my MC survives as a runaway]. But for many, the snap had taken the best people out of their lives.”

Story

Before the snap, 17 year old Jake [placeholder name] lived for his little sister. Protecting Emily from their abusive and neglectful parents was everything to him, but then she vanished in front of him, dissolved into particles and then just… gone.

They had been home alone when it happened. He saw the explanation on the TV, half of everyone vanished indiscriminately. The snap had taken Emily but not their parents. He had no reason to stay there anymore.

So, a grieving Jack decides he will disappear too. They’ll never notice. The snap is a perfect opportunity and cover for a runaway.

Like, there's no reason for 99% of the universe to even know about Thanos and his plan. There are six infinity stones, most of which are located on Earth/Asgard/in our Galaxy, so why would he bother with visiting any of the rest of the billions of galaxies? Even if he murdered his way across every planet on his quest, that's still a tiny fraction of life, and if it is NOT a tiny fraction, why does he need to bother with the stones in the first place?