The singular problem with Pascal in contrast to C was that C is a much more generic language than Pascal with a more flexible typing system.
In Pascal, notably, I/O is a first class concept, with direct, and "special", support in the language. The original Pascal typing system wasn't flexible enough to handle outliers such the I/O system which need to support multiple types.
nil is a keyword in Pascal because of the strict typing issues.
In C, there was no concept of I/O, and when implemented, it was done using the standard C structures, functions, and typing system that had no special support within the compiler. The I/O system was no different than any other function call.
This made C both more extendable, and more portable in the large.
Obviously, later Pascal implementations added better support to the compiler to handle special cases like I/O, and loosening up the type system. But the competing implementations just did things in different ways, thus limiting portability.
While you couldn't trivially port a Mac C application to Windows, due to the dramatically different interfaces to the overall environment, you could readily port the business logic parts that did not have those dependencies.
Now, since C the language left things like I/O up to the implementors, there was the potential for the world to run a gamut of implementation of core functionality. In fact a lament from the author of BDS-C, for CP/M, is that when he had his first exposure to C, the library he had access to differed in significant ways from what K&R eventually published. That's why his BDS-C compiler can't necessarily compile K&R compatible C programs (he had other incompatibilities as well, not simply the library). So, that was an early example of that phenomenon.
But K&R came out early enough, 1978 I think, and it was such a simple book, "heck, why not just implement this and move on". We need an I/O library, here's a I/O library.
Yet, Windows, Mac, and Unix, all had their own, internal I/O libraries upon which Standard I/O were implemented upon. This demonstrated the flexibility of the language to let developers expose the functionality that they wanted to offer, yet still retain some modicum of portability for those who were interested in that.
The early Pascals were very good. Borland's work, Think/LightSpeed Pascal on the Mac, plus all the work Apple did. UCSD P-System was quite advanced.
But, as with everything else, they were just a bit too early. C became popular because the industry had experience with Pascal, and folks enjoyed the portability and flexibility that it offered.