If TATA's really made the NANO, why not a Marcopolo bus?

BMTC has bought 2 Marcopolo buses made by TATA's in India, under collaboration with a Brazilian company. Priced at 55 lacs, these are cheaper than the 72 lac Volvo. And looks amazing.

Tata's have been into car production for, maybe 10 years and they have the technology, guts and finances to independently develop a small car from scratch and then go into production.

If this is true in every sense of the word, WHY then did they not make any improvements to their existing range of trucks, which they have been churning out senselessly and unimaginatively for the past several decades?

What does it take for a company which can make a Nano from nothing, to make a low slung, passenger bus ( not a body and seats strapped to a lorry chassis) from an existing facility. Will this not be easier and cheaper than collaborating with a foreign company?

Or are we just seeing a part of the whole picture?

If collaboration was the only way TATA's know to introduce a superior product, faster and cheaper, why go through the farcical  and expensive route of innovation and product development for a car? There are thousands of small cars readily available for collaborative manufacture?

What is the truth?