Mexico refused to recognize the independence of Texas in 1836, although most major nations did so.
The answer is simple: for the same reason that it did not recognize Kosovo's independence.
Mexico was among the first nations to recognize Lebanon's independence in 1943.
Canada, for example, was the second nation in the world to recognize national independence of modern Ukraine.
Egypt was one of the first countries to recognize Indonesia's independence.
Argentina was among the one of first countries to recognize Morocco's independence in 1956.
Most of the world's countries immediately recognized its independence.
The two organizations signed an agreement in January 1989 recognizing their independence.
Apart from Mongolia, however, no other country recognized its independence.
It was also read as being likely to lead to more countries recognising Kosovo's independence.