> But they do! Pre-C99 there's no way to say "I want a type that's at least 32bits and as fast as possible" or "I want a type that's at least 32bits but as small as possible".
I stand corrected on that point.
> Clearly people were not fine just using the minimum requirements of the standard.
Most of these typedefs are used to interop with some other standard or file format that requires that many bits exactly.
But even then I would argue that there was an overuse of such typedefs in C. I can think of several reasons for that:
First, there's a general lack of awareness that C does in fact provide "at least N bits" guarantee for most of its types. This comes up pretty often in questions on StackOverflow, and apparently there are still enough people surprised by the fact that e.g. long can never be 16-bit.
Partly, I think, it's because of the historical mess with int. Obviously, int is what people use by default, and the fact that it was 16-bit on many popular architectures in the past, and then became 32-bit on their successors, resulted in much broken code. I think that the lesson many took away from this is that all integer types in C are similarly broken, and switched to int32_t (or equivalent typedefs) just to avoid having to think about it.
Partly it's because of 64-bit ints. Standard C didn't have a 64-bit type for a long time. Popular implementations provided it as an extension, but in different ways - long long in most Unix compilers, __int64 in 32-bit DOS and Windows compilers. So if you ever needed 64 bits, you needed a typedef for that. Since most devs work on systems where word sizes are 8/16/32/64, they did the simplest and most obvious thing, and defined something like int64_t (as opposed to int64_least_t) - it just didn't occur to them that something beyond that was needed. And that set a precedent.
Then there was the part where long was made 64-bit in LP64 model, which meant that portable C had no "at least 32 bits, but no longer than it needs to be" type until C99. With the precedent established by int64_t, the logical step was to add int32_t, and int16_t as well for good measure.
And that's how we got where we are today. I would still argue that most of those libraries that use int32_t and similar types don't strictly need it. It's just a combination of historical factors, and also the fact that platforms where such types do exist comprise the vast majority of platforms, and all platforms that people care about. So there's no particular incentive to even think about how you'd write code for something else - why deal with the extra complexity, if you can just wave it off? Can't blame anyone for that.