I don't know how common this phenomenon is in India, but anecdotally, most of the Tamil people I know who graduated from college can barely read and write Tamil

I don't know how common this phenomenon is in India, but anecdotally, most of the Tamil people I know who graduated from college can barely read and write Tamil. They have no problems speaking it, but they'd struggle to write an essay in Tamil, let alone a thesis. No such problems in English, obviously. You often hear the concern that regional languages could disappear because most parents would prefer that their kid studied in an English medium school.