The 1930's are often held up as a golden age of travel writing - Robert Byron, Peter Fleming, Fitzroy Maclean, etc etc.
Two reasons, technology and access to exotic and remote locations. I'll turn to technology second but access is one of the keys.
Before first world war (actually before the Russo Japanese war) much of the world not part of the French and British colonial empires had been closed to foreigners. Both tsarist Russia and the Ottoman empire were not exactly welcoming and China was definitely closed, meaning people did not have much in the way of opportunity to visit places that were definitely foreign - ie where opportunities to interact with people from a background not unlike your on were limited. I'm having difficulty expressing this succinctly, but if you've ever been to bath house in Morocco where all the signs to customers were in Arabic you'll know exactly what I mean - the slight edginess as to whether you've understood what is going on, and the surprise when something different happens - that's foreign.
And also - post 1919 - there was a great hunger for people to understand what was happening with the new world order - to understand the rise of Japan and the changes in Manchuria, and the great changes and convulsions in Russia, and whether the Soviet Union represented some fundamental change in the way the world worked.
At the same time, travel to these places, while difficult, was not impossible. People could travel around the Soviet Union before the purges and the terror with a degree of freedom, even if they did have to agree travel plans with Intourist, and access to China was relatively easy with substantial foreign communities in Beijing and most notably Shanghai in the international concession.
Also the mechanics of travel were easier. Contrast Peter Fleming's admittedly gruelling journey by truck, train and horse from Peking to Srinagar with the journey of a British official thirty years earlier to the same area who had to walk or be carried by sedan chair such were the state of the roads. Fleming chose to travel part of the journey by horse to both visit reote areas and dodge officialdom. He could have managed most of the journey by truck, as did Joseph Needham a few years later, except for the final stretch across the Kashmir border to Srinagar.
People could travel to these areas by road and by train, and road meant by truck and car. The roads were open and it was possible for people to drive from London or Berlin to Tehran or Kabul. Likewise the remoter parts of central Asia were accessible by train via Moscow across what is now Uzbekistan and Kazakhstan.
So the technology of travel was easier. So was photography. The first 35mm Leica cameras revolutionised photography - cameras were no longer clumsy things and crucially no longer used bulky films or plates - a 35mm cassette could hold 36 pictures - more than twice as many as a 120 or 127 film roll and less vulnerable to damage or accidental exposure. I've not used one of the early Leicas but I have used Fed 5b Leica clone dating from the late 1970's.
The results are pretty impressive, the camera is almost indestructable, and while at around 600g it's not light, it's not a great bulky monster either. It also crucially doesn't need batteries. Unlike later 35mm cameras it doesn't need a power source for range finders, light meters or autofocus. It does of course require you to do a bit more work, but with the slow films in use then, say 50 ASA, you had a degree of leeway if you guessed wrong.
The other great key technology was the portable typewriter. Probably about twice the weight of a laptop, but packed up probably no bulkier than a laptop in a travel bag, it allowed writers, who were essentially journalists, to work on material, type up notes and copy just about anywhere. Again crucially they didn't need a power source, and could work in places not connected to the power grid, or on trains etc.
It also meant that they could travel relatively light - always a consideration when having to haul your own luggage part on and off trains, or cram it into tuktuk or similar as I can attest from personal experience travelling through Laos at the end of 2005.
Also, the typewriters and cameras were a good deal tougher than a netbook and a digital camera, and would survive the occasional dunking or exposure to snow and cold.
So, changes in technology and improved opportunities for travel, plus a heightened public interest in what was happening in places previously off the map conspired to provide a combination of circumstances that provided a marvellous opportunity for both photojournalism and travel writing.