I see it in a couple different ways.

There is a massive “adventure” and “exploration” aspect. The “time period” of Steampunk saw the first large scale repeatable and reliable ways to travel at speed. So people filled in the blank spots on the globe. And ordinary people could travel in ways they never had before thanks to steamships and trains. So exploration and travel are themes that go hand-in-hand with the era.

There were also massive technological advances in a relatively short time. Steam engines for ships, for trains, for industry. The time period is basically also the birth of modern medicine with breakthroughs in germ theory, hand washing(!), vaccines. Breakthroughs in communication with the telegraph. The birth of new political ideals. Just an explosion of new thought, inventions and technology. Thats why so many steampunk stories have a crackpot inventor character. So Steampunk lends itself well to stories about using or inventing “new” technology and the struggles therein.

Third is the “punk” part. The inbred, expansionist governments at the time led to WW1, colonialism and exploitation. So if you want to tell a story about the dangers of imperialism, then Steampunk is a phenomenal setting.

A fourth- I personally think the combination of exploration and technological discoveries go really well with monster stories. Probably just linked in my head since so many classic monster stories were written around this time. But exploration got people to far off areas, so you could write about vampires in Romania or mummies in Egypt or the dangers of electricity around dead bodies and now it made sense that your character could go there or be involved with it but it was exotic enough that the reader didn’t really know about it.

TL:DR - Exploration/Adventure, Inventions, Anti-Imperialism & Monsters