Actually there are several reasons. One being that IH actually lead the way with inovations that it took other companies decades to adopt. More than 2 cylinder engines, Diesel powered farm tractors, row crop farming, shift on the go transmissions, hydrostatic transmissions, ceramic friction materials in clutches and etc. I can't verify that IH was first in all of these revolutions, but were responsible for many. And these only include tractors and do not include farm equipment designs.
Another reason can be found in the Nebraska test results showing time and time again how they out- preformed other similar hp sized models built during the same time period in torque rise and HP hr/gal figures.
As a mechanic that works on many brands of pre 1985 tractors, I can verify simplicity of designs with very few "Rube Goldberg" contraptions found in other "popular" brands. (Like the SCV, 24 volt split load electrical, pony motor starting and Permaclutch in JD).
The sheer numbers of IH tractors are still alive and well and farming around the world today in spite of the fact that the newest International tractors are now over a quarter of a century old, testify to their durabily and usablity.
Although I am an admittedly an IH fan, I will be the first to say that they and their products were not always THE best, but overall you would be hard pressed to (leaving opinons behind) honestly find another ag equipment producer that matched IH for innovation and contributions to designs and manufacturing proocesses that paved the road to our country being an agricultural giant that it is.
I don't have any particular brand allegiance. Does it do the task and is it reliable are my criteria. I see Tee shirts and decals that talk up Deere killers and the like but rarely any of the like announcing they're IH killers, perhaps because that's already been done.
Even Deere knew they had pushed the two cylinder too long but, although primitive, they were fuel efficient. The 720 had fuel figures better than anyone. As for pony starting, International had start on gas, run on diesel about the same period as Deere was using pony motors. Cat used a pony as well. I still have a 620 gas and although it's mostly retired, it will still start in any weather and put in a day's work.
I bought an 86 series, my first IH other than industrial, because it was a cheap and reliable power source, not because of any technology as they were well behind the power curve by then. Deere had a reliable power shift for years while IH was still flogging the TA. The 86 is an ill-shifting machine compared to the competition. I like it because it's simple and suited to the task I assign it. When it comes to maintaining old stuff, simple is good. It really cannot be compared the competition of the same period for technological advances. If it could, perhaps they, IH, would still be in business.