The biggest issues were :

1. Bengali vs outsider image. The BJP did not have a homegrown leader who could go up against Mamata didi
2. Minority religion of 30%+ vote complete consolidation in favour of the TMC
3. The majority Hindu vote did not consolidate for the BJP Most of us are left Liberal secular Hindus due to the long communist rule history
4. Defectors from TMC joined BJP and hurt its credibility. People who were angry with the incumbent due to the corruption and violence lawlessness could not justify voting for the same people switching camps
5. Long drawn poll phase and too many central leaders visiting Only Modi is popular no one else of the central lot
6. Covid second wave affected the last three rounds of voting and people were angry at the abysmal situation
7. Over reliance on rhetoric and not building organization strength to handle vote machinery across the state
8. The BJP could have done far better if they had focused on their core worker base and kept the message fixed on development instead of polarization