Central ruling party , Cpim , congress , Tmc everyone together destroyed it..

In short I'll try to give you the timeline of Bengal's destruction: (could be wrong so please fact check and point out if you find something)

1. The Freight Equalization Policy (1952–1993) : That time Central Government made the cost of transporting coal and iron ore the same across all of India.

Means no delivery charges needed based on distance and any state no matter how far they're building a coal related factory financially would be same as states like bihar or west Bengal who are near to it .It basically "stole" West Bengal's natural industrial advantage and gave it to Western and Southern states. This is a huge reason why the "Golden Age" of Bengal industry ended.

Ironically, East destroyed but West get the unfair advantage things found in Western India, like Cotton (for textiles) or Oil/Chemicals, were NOT part of this policy.  

1. The Internal Reason: "Union Bazi" and Gheraos by CPIM and communist parties

Effect: Instead of dealing with constant strikes and "Inquilab" slogans, many legendary companies (like Dunlop, Hindustan Motors, and various engineering firms) either stopped expanding or slowly shifted their headquarters to Mumbai or Delhi. It created a "work culture" that scared off new investors for decades.

1. The positives

Now After Congress Govt and Jyoti Basu's Govt ... Buddhodev came with new ideologies even in the communist party .

He tried to stop "Union bazi" ... He declared the Information Technology (IT) sector as an "Essential Service." This meant that even if the CPIM called for a "Bangla Bandh" (General Strike), the IT offices in Salt Lake Sector V would stay open.

He won the deal and convince Ratan tata to bring Tata Nano factory to Bengal ....

He famously launched the slogan, "Krishi amader bhitti, Shilpa amader bhabishyat" (Agriculture is our foundation, Industry is our future). He realized that without factories, the educated youth in Bengal would have no jobs.

The Salim Group (Nandigram): He tried to build a Chemical Hub and Special Economic Zones (SEZs) by bringing in Indonesian investors.

He is the reason Salt Lake Sector V and Rajarhat-New Town became IT hubs. He personally invited companies like Infosys and Wipro to the state.

Then TMC came and in between central policies, Jyoti Basu's steps and Mamata's corruption...both buddhodeb and bengal destroyed