Elevator doors opening straight away to offices/private homes.

Well, in my building the public only has access to the first and second floors. After that you need a identicard that you hold up to a magnetic reader in the elevator. It won't go to any other floor until you've waved the card by the sensor. Pushing any other floor button does nothing otherwise.

This...^^^^

I once worked in a building which my employers owned, all except the 4th floor, which was leased out. You could press the 4th floor, the doors would open, you'd be in their manned reception area. After hours the reception area would be unmanned, and the doors behind reception would be locked. After a certain hour, the elevator wouldn't open on that floor unless a swipe-card was used.
My employers had their reception area on the 3rd floor (1st and 2nd, AIR were for the computers) which was the only floor the public had access to. Anyone could press 3, and be allowed out onto that floor. Front desk staff were supposed to stop strangers and ask them their business, and direct them. No-one was supposed to wander around unescorted. If you wanted another floor, you had to have a swipe card, or an escort with a swipe card.
There were constant warnings about letting strangers off on other floors.

Ditto with the magnetic reader. I can only get to my floor and to the basement.

Yep, where I used to work the company rented the whole building. You could go to reception during office hours, all doors leading out from reception had electronic locks. To get to any other floor or to get in after hours you needed a key card.

I've worked in multiple buildings where, if you were able to get inside, you were free to roam. In other words, no elevator security.

I've been in buildings where the doors open to anyone but there were secondary doors that were locked to prevent admittance, i.e. you were in a lobby on an upper floor. Security cards were needed to go further...big glass double doors to the front and small wooden doors on either side.

I've also been in buildings were I was able to go right to the unmanned (or womanned) reception area and even beyond after hours, but the building had security so no one was left in that didn't have business there. In that case we were required to sign into the building but then had free roaming rights. Cameras kept people honest.

Another point, if you look enough like you belong then no one really bothers to check.

I've strolled past security into research facilities, medical labs, police stations...there was a security guard at one courthouse that used to wave me around the metal detectors.

People have distractions and emotions and they'll ignore their duties if they want to impress, be kind, or just not bother...if you look like you belong.

It's your world. You're in control

Where I used to work we shared a building with a couple of other companies. We didn't have a fancy elevator, but we did have security doors on every floor. Anyone could take the lift to any floor, where there was a tiny lobby, but you needed a card to get through the doors.

A friend lives in a high-rise where there is a separate elevator for each stack of flats. He enters the elevator and it opens onto a small, stark room that has a set of proper locking front doors to get into the actual apartment.

I'm not sure how he rings in visitors, as I've only ever been there when I arrived with him.

Anything you want. There's a thousand and one ways this works.

A note. If the person lives in a loft, the elevator can't go all the way up, since there's no space to put the motor and the gears. There are elevators that push rather than pull... but then you're talking James Bond villain type house.

The first answer was best, but I have been in a few buildings where you could get off on any floor, but then you would face locked doors and/or receptionists on that floor.

For departments other than IT and law where I've worked, once you pass the front security desk you are golden. On camera, but golden. We always roamed the floors above IT to raid the better-paid folks' free coffee stations.

Security saw us, but they were our smoke buddies, so we'd just bring them things, too.