Unfortunately, the commerce stream teaching is very very average in India. People who passout have very little knowledge of anything, lower level IQs and general understanding. I have interviewed commerce graduates who quote their favourite subject as economics and do not know the full form of GDP.
Secondly, because of better job prospects, brighter students after 10 and 12th prefer to take engineering and medical. Therefore the average quality of students admitted to engineering are better than commerce. That does not mean that bright students do not join commerce or all commerce students are average and engineering students bright, but on an average the input quality in engineering is certain better. Further, engineering studies are much more hectic, detailed, strenous, analytical, logical and knowledge oriented. For your information they do study economics in many colleges. The amount of studies they put in is far far far more than a commerce student which helps develop their overall perspective, knowledge, and IQ.
If job prospects are better across stream, people will choose streams according to their own interests and that will ensure bright students join all streams. Otherwise, this preference will continue.
Again, I do not mean commerce is bad, but just the situation in India is such. Finally, commerce should be compared to bsc and not engineering which is a professional and advanced course.
