- The economy is what ultimately matters to many people, and the impression is that the economy has been bad for the last 4 years under Biden but was better under Trump. The actual data is more unclear and confusing, but the average person has this impression.
- Harris wasn't likable/charismatic enough to many people, and was largely supported for her policies first and her personality second. Trump, on the other hand, went on a lot of longform podcasts, worked at McDonalds for a few hours, and generally seems more "human" to the average person.
- A general sense of rage/dislike/push-back at "elites" in Washington DC, the coasts, the mainstream media organizations, etc. If you google "trust in government" or "trust in media", they will elaborate on this issue. Trump, although a billionaire from NYC, is generally disliked there and is perceived as being an outsider and rebel vs. the elite group mentioned.
- Some protectionist policies Trump claims to support will benefit people in key battleground states like Ohio, Pennsylvania, Michigan, etc
Ultimately it comes down to two things, IMO: personal charisma and the economy. Everything else is only relevant in close elections.