I don't believe that the "software Agile" was very successful because it was, from the beginning, "better" but because it came at the right time and because the environmentof the rapid penetration of devices using software in our lives.
Many Agile practices, like iterative and incremental and test driven development, were used for decades when the Manifesto was published. Some Agile frameworks XP, DSDM and even Scrum) were already used for years.
The big enablers were the Personal Computer, the cloud, mobile devices and last but not least the Object Oriented programming. Not only that software development become a widely spread occupation and done more and more outside the traditional "Computer Office" but with Pascal and later c the way of thinking was different. In 80s computer time and technical performances (processing power, memory, storage) were the significant impediments. I remember the PDP 11 with 16 terminals and th3 256 MB hard drive. Then we had the first PC in mid 80s and what took one day to run on PDP took less than 2 hrs on the PC, we didn't need punch cards but we had to partition the 20 MB hard drive because it was too big.
Software is no longer bough as a product like in 2001, nowadays we consume software services (Facebook, tweeter, Uber, Amazon, eBay) or we rent it. However Agile values and principles transcended software development and practices developed in manufacturing are adapted to any projects with Agile becoming an option to be considered for any project,