Not just that Turbo Pascal had modules, but that it had enough of the market that it would have been hard for Modula-x to get a foothold, even if Wirth was a salesman, which he was not.
Borland had a Modula-2 compiler, created by Martin Odersky of Scala fame.
They decided to focus on Turbo Pascal instead.
Turbo Pascal units are based on USCD units actually.
Outside MS-DOS, Modula-2 had better chances, but since it was MS-DOS that won the 16 bit wars, it became irrelevant, as the only major alternative were UNIX clones were C and C++ ruled.
Modula 2 was quite popular on the Commodore Amiga where C compiler where a bit so so (or very expensive) for quite some time, but in the end the PC won.
I agree: There were several successful Pascal systems that (a) pretty much had the commercial market for such languages saturated and (b) had pragmatic solutions for areas such as I/O.
I/O in the original Pascal definition was particularly unfortunate in that it both needed ad-hoc mechanisms and was not particularly expressive. Modula-2 improved on this by being capable of doing I/O without ad hoc mechanisms, but it was still not very expressive.
But if you bought into the more purist Wirth vision, and especially if you tried to use the language as officially defined, Modula-2 was a much nicer language than Pascal.
