1) being the biggest conventional doesn't matter when there are bigger unconventionals that are competing at lower break evens. https://www.adn.com/energy/article/prudhoe-bay-loses-top-spot-among-us-oil-fields/2015/04/07/

2) check out the latest SEC filings and reserve numbers from BP, they don't even support a 20 year life at current prices, much less past 40 years. 

3) people invest when it's financially viable. They don't invest when it isn't, and they don't stay on the edge of the swimming pool when there is money to be made. How could they concurrently be the greedy businesses you proposed while turning down profitable exploration at the same time. Doesn't pass the smell test.