Simple explanation: Because the phones are so small.

Complex explanation: There's magic done inside a Western Electric phone, which allows what you say and what the person you're talking to says, to travel over the same set of wires. It's done with a special kind of transformer, called a "hybrid coil". In modern phones, it's called a "network."

Those candlesticks contain only what's in the handset of a "normal" dial phone: a microphone and a speaker. And the hookswitch. Everything else is in that box. And they've been able to make it smaller over the years.

That was my first thought. Amazingly, some of those buildings lasted into the 1960s - much of the then-called War Department as well as the Navy brass were housed in them until the Pentagon was built at the start of WWII. I believe the CIA used a number of them until Langley was built in the early 60s.

Spittoon and phone ringer boxes. My antique 1926 Western Union phone still uses a ringer box.

Wiring for all of our electronic devices is still a problem today in the office environment.

They may not be the most comfortable in the world, but they're about as solid as they come. I'd be willing to bet they're still around!
We actually had a dining room set composed of chairs my dad had beautifully refinished with chairs that look very similar to the one on the far right. They came from a law office many, many years ago. We thought they were great!

Office design by Piet Mondrian.

The office seems to be rapidly built and outfitted space intended for temporary use. Washington went from a sleepy Southern town to a metropolis overnight as a result of World War One.
The half silvered light bulb is an interesting touch. We still use one in our kitchen.

After viewing hundreds of interior shots on Shorpy over the past several years, the majority of interiors look like the floors were polished with gravel and the furniture with chains. Nice to see a decent wood floor and new furniture.

I love the way the desk is not squared in the room; it reflects the odd bit in the corner. Having the basic layout "unsquare"in this way bodes well for the artistic integrity of the team's charts!

Why does each phone need such a large box connected to it?

[It's called a ringer box. -tterrace]

The wide desk with two kneeholes is known as a "Partners' Desk". Great opportunity to contemplate your partner all day.

Looks just like one you could buy today. But the phone boxes attached to the desk are huge. Wonder why they were so large.

Believe the bureaucrat looked unhappy because with the war over, his job would no longer be needed.

My, how file cabinets have changed over the last hundred years!! (That's a joke)

All the graphs are pointing upwards!

Four months after the armistice, and we still have a war poster up ridiculing the Kaiser!

All those spiffy charts, and generated 70 years before Power Point!

This looks so typically bureaucratic (even the shade on the lamp matches the walls!) that that spittoon sticks out as an oddity. He does not look like the type who would partake in a bit of the ol' Mail Pouch.

To save money instead of buying a desk for each of us we'll just get a really wide one for two.

Hold on while I spit.

Even the spittoon is polished. And all trends are positive.

That ceiling at least is about 30 years ahead of its time--all it needs are the fluorescent fixtures to look up to date today.