Speaking a national common language and another mother tongue doesn't have to be mutually exclusive.
Singapore is a good example of this: they adopted English as the common national language, while having a bilingual education system that preserves the mother tongues.
I’d also say it’s not like they’re really going around saying you can’t speak Cantonese at home. The issue is that there is natural attrition when school and official things are in one language (not that different from what the article describes).
There is no preservation of mother tongues. Languages are assigned along ethnic lines in the name of nation building.
yellow → standard Chinese
native → Malay
brown → Tamil
If the father is a Fujian Hakka, the children will learn standard Chinese in addition to English. If the father is from New Delhi, the children will learn Tamil in addition to English. If the father is from Lisbon, the children will learn English only.
Singapore is a good example of this: they adopted English as the common national language, while having a bilingual education system that preserves the mother tongues.