Maharashtra, Gujarat and Goa have some of the highest levels of economic/industrial indicators but have been traditional BJP strongholds, whereas the BJP has never formed a government on its own in Bihar, arguably the most backward state in India. They also struggled in UP, another supposedly backward state, until the Modi/Shah/Yogi trio managed to crack the code through a combination of savvy political engineering and delivery of governance on the ground. The southern city where the BJP is the strongest is Bangalore-the most economically developed city in the region. Even in Delhi, the BJP has swept the last couple of Lok Sabha elections and it is the AAP, and not the Congress, that has been defeating the BJP in local elections.
Again, this looks very different when examined in detail.
It is far from coincidence that the strongest locations for the BJP have been the Brahmin-first locations. Let us look at the places you have mentioned, with this in mind.
Maharashtra gave the BJP a strong base from Nagpur and from Pune, both strongholds of the Brahmins. The success in Mumbai/Bombay was not that of the BJP, but of Thackeray's movement to rid Bombay of the ubiquitous south Indian.
Gujarat is an electorate that I would cite as a prime example of the cumulative effect of the RSS grassroots campaigns conducted against the backdrop of a steadily degenerating Congress culture.
Goa was a struggle between the Portuguese Catholic pockets and the increasingly stronger Hindu pockets, dominated from the outset by Konkanastha Brahmins (the Deshastha having sealed up Pune and Nagpur already).
Bihar was never a possibility because the caste line-up was already in the pockets of the Congress, through the Mishra brothers from Mithila. Subsequently, their loss of power was seized by the OBCs.
Both Bihar and the UP, it may be recalled, were places that were most strongly affected by the storm that followed the Mandal Commission report. Perhaps it is better to view the loss of UP to the Sangh Parivar as the increasing moral decay of the Congress creating a vacuum, that was not completely filled by the Yadavs and was quickly pocketed by the Sangh Parivar.
Bangalore, for that matter, Karnataka, is a perfect illustration of what I am alluding to. Bangalore itself is riven by the presence of the Kannada Brahmins in Basavangudi - you will find that the constituency has gone to the BJP - and of the domination of Iyengars (east of 8th Main Road) and Konkani Brahmins (west of 8th Main Road), that meant that Malleswaram and north Bangalore also went to the BJP. On the coast, the Udupi belt was no surprise, nor the Bunt-dominated gang war zones of Mangalore, or the very strong pockets in Hubli and Dharwar.
Think about it.