In many, probably almost all US cities any downtown areas is used for "business" - i.e. commercial offices. The living pattern is you wake up, drive anywhere from 10-40 miles, 10 minutes to 2 hours, and you park your car in a parking garage and then walk a block to a skyscraper where you go up into an office area.
After World War II the US built highways that destroyed most cities. Take a look at the 1949 image and then the 1981 to get an idea [1]. The root cause of many of America's continued problems, ranging from racism and classism, to oil and car dependency are linked to what we did over the years.
Most US cities have a central business district that is majority commercial office space, with just enough retail/dining to let workers take lunch breaks. These are the areas that are dying. No workers, so the surrounding retail/dining is failing.
Back in the 50s/60s, white flight was a problem for cities - most of the middle class, white families moved to the suburbs. Most cities didn't have a large tax base that lived inside the city. That started to change over the last 20 years or so. Couple that with off-shoring or moving of heavy industry out of city cores and cities will struggle financially without white-collar/knowledge workers commuting in and spending money.
Western Europe doesn't have the same level of suburban sprawl.
Edit - the white flight I mention is closely related to the inner-city highways mentioned in the sibling comment. Suburban workers needed to get downtown, so (usually minority) neighborhoods were split in two or destroyed to built highways from the outskirts into the CBD.
I grew up in Houston, Texas. As a kid I remember downtown as being 1. Big office buildings with parking garages. 2. Concert halls & auditoriums. 3. City and county facilities. 4. Restaurants catering to the visitors of the above. 5. Sears & Roebuck department store.
Nobody lived downtown, and most of it was dead after working hours. Most of the office buildings had no street-level retail shops at all – there was no reason to go there except to work, or in the case of 2-3 of them, to visit the observation deck on the upper floor. The small area where (2) were concentrated didn't even have much in the way of restaurants or shops open. If you worked there, you drove downtown in the morning, came home in the evening. If you wanted to a concert, play, or ballet, you drove downtown, enjoyed the show, then drove home.
There was, and is, one unique thing about Houston. The tunnels. There is a network of underground walkways and areas connecting many of the buildings. There are some restaurants and shops, and during the lunch hour the area was packed. But you couldn't get to those tunnels without going into one of the office buildings, and they were only open working hours. Most of the stuff in the tunnels opened at 10am and closed at 2pm.
Predominantly, downtowns will have a financial, medical, and government district.
Government: police, city hall, courthouse, administration for city, county, state, and federal agencies.
Medical: usually a major or university hospital with various outpatient services in nearby.
Financial: banks, banking services, property and financial services.
Typically, just these 3 things were enough to compromise over 50% of commercial downtown properties. We're not even approaching cities that have a major HQ or specialty (manufacturing, tech, media, print).
For a lot of cities once a major tenant moved out, they really only had government and medical as the city's economic engines.
My city I've watched transform from being a violent, crack infest dump to a very desirable, fair weather place to be. And because of the loss of so much commercial business in the 90s they managed to avoid the glut of commercial properties. We pivoted to residential/mixed-use development in 2003 and it's really paying off now.
Our downtown doesn't do anything in particular (except maybe crypto) except be a place for socializing.
