It's basically a balancing game, the majority of the major hydrocarbon reservoirs are in maturity stage quite often depletion. As technology increased, the efficiency and types of reservoirs we can extract from has increased but these are generally smaller reservoirs, as the biggest ones are the easiest to find (thus drained first). Currently we're in the seasonal cycle of where the production out ways demand in quite a freak manner of luck (or bad luck). Oil reservoirs are extremely expensive to develop and run and even more expensive when your not running from it (it literally costs you millions per day), so no company frankly wants to stop production. That's why it took OPEC so long to reach an agreement.
Still we're at a point we're most major fields are making the best of scarce and starting to deplete resources, which is why more potential oil is still seen as appetising even in this situation.