Yes it's very common to rent from a company rather than individual landlords. Some of these companies are massive managing hundreds of thousands apartments. Many of the building are specifically built as rentals and all units are for rent hence there is often a leasing office somewhere in the building.

OK. Here such companies just have one central office per city/region, no building-specific ones. The largest companies here manage "only" tens of thousands of rental apartments, though.

How are they handling visiting the grounds/future apartments for interested renters? That's one of the main duties of the leasing office people in the US. When looking to rent one visits many such places and asks the leasing office people various questions while doing so.

Typically by making an appointment.

Scheduled public presentations, or appointments.

I think you would be hard-pressed to find an apartment complex without a leasing office. I have never seen that in the US. Mostly I think they are there to handle showing people around and finalizing leases. They also can handle maintenance disputes and forward complaints to the right people.

Also, for the sake of those outside the US:

Heavily weight the first impressions of the leasing / office staff to determine whether you WANT to live in an apartment complex: As stated above, these will be the people you will deal with for anything from clogged drains - to being unable to pay rent on time.

In short: you want to make sure they are friendly, professional and courteous -- or it may ultimately detract from the perceived quality of living in that Apartment [0].

[0] - I lived in 6 apartment complexes from time I was a broke student to young professional with a family.

Commonly apartment complexes here (Finland) are owned by building-specific limited liability housing companies that do not make profit, with shares corresponding to apartments. Those shares are then owned by various individuals or rental companies, so a building office makes less sense.

But if a rental provider company owns the complex outright, they still don't have building-specific offices, but just one central office per city/region.

That arrangement would be considered a co-op in the United States.

While such an arrangement is possible and legal everywhere something like 95% of all co-ops are in New York City.

What's the upside for the company that owns the building?

It's fairly common in newer and/or larger buildings; walk-ups and buildings with a single landlord don't usually do things that way. But a lot of people moving to big cities around here are probably familiar with the idea. They also handle maintenance requests, showing people units, and sometimes things like community events.

The USPS does also have package lockers - larger boxes with keys that get left in your mailbox - but they aren't universal and companies like Fedex and UPS rarely have access to them. You can also have things held at the post office.

It's not that there are no other ways of solving the problem, it's just that the lockers are convenient and requires very little planning or forethought.

Many states require an on site property manager for larger buildings. So it is normal for them to handle collecting rent, screening tenants, signing leases

Is this the same thing as a concierge? I've seen a few apartment blocks with them in the UK, but it's rare.