What's the real reason why the future Universe 7 has to suffer Zamasu's evil purge instead of the present?

In Dragon Ball Super, although Zamasu could easily take over his own universe, he seems more interested in wiping out Universe 7.

Zamasu’s ambitious and nearly successful plan to eliminate the Human Multiverse became the most complex plot in Dragon Ball Super. A story involving many concepts such as body swapping, time travel, immortality… has left many people confused. One of the most curious questions is that if Zamasu is from Universe 10, then why did Universe 7 suffer his evil conquest. Or why is it Universe 7 in the future and not the present?

As we know, Zamasu is a former apprentice of Universe 10 Kaioshin. He previously developed hatred for humans after witnessing their endless violence and selfishness. When Gowasu, the current supreme god of Universe 10, reminded Zamasu that the Kai gods were forbidden to interfere in human lives, he began to develop a grudge against the other gods.

The climax is that after meeting Goku, Zamasu’s attitude and personality officially changed markedly in a bad direction. He believes that a normal person like Goku daring to challenge a god is a terrible insult. Furthermore, it is unacceptable for a human to gain such great power. After learning the secret of the super dragon balls through Zuno, Zamasu hatched and carried out his intention to destroy humanity. For that reason, he set Universe 7 as his first target.

Besides, destroying the entire human race in the Multiverse requires great strength, and in fact Zamasu himself is too weak for such a large-scale coup. After time traveling and stealing Goku’s body, Zamasu gained the power needed to carry out his genocidal plan, but it was not enough to defeat the Gods of Destruction or the Angels. However, Zamasu discovered a truth, it turns out that killing a Super Kai – someone with quite weak strength, will also end the life of the corresponding God of Destruction and cause the Angel to no longer exist.

After the God of Destruction Beerus interfered with the plan by killing Zamasu in the present, he could do nothing in the main timeline of the series. So instead Zamasu traveled to Future Trunks’s timeline, where another version of him existed. Also because it was here that Super Kai Shin lost his life in the battle against Majin Buu, leaving Universe 7 of the future timeline as the perfect place to begin the genocide plan.

In this timeline, Goku Black and Zamasu successfully purged the universes by killing Super Kai from one universe to another, so here the Gods of Destruction and Angels no longer exist. again. While it is unclear whether Zamasu wiped out all life in the universe or simply killed their gods, it is clear that Universe 7 was seen to be completely destroyed.