The Humans spent most of their time trying to kill each other.

Another writing prompt:

Humans, despite their boundless creativity, took longer to develop space travel than other alien civilizations. That’s because they spent most of their resources developing more effective ways to kill each other

Historical record 62,8845-A32 “Human introduction to galactic civilization”

AKA “What do you mean we are the strongest military race in the galaxy?”

The Humans spent a long time before they took their first steps into the galaxy. Most species were taking their first steps on their closest extra-planetary body about 400 years after they had their industrial revolution. This was an average with some species taking less time, others more, depending on circumstances and problems with planetary conditions.

Humans took close to 1,250 years after their industrial revolution to get a foothold in space. They had made small steps forward by visiting their moon or closest viable planetary neighbor but their constant infighting kept disrupting their steps forward and at times halting any advances outwards.

And it wasn’t just military conflict that caused problems for them. For a while they were too busy trying to combat the world wide climate changes they had been causing and ignoring, and they had to put all their efforts into fixing their mistakes instead of expanding outwards into the closest star systems.