instead of lowering prices to encourage more consumption to increase profit margins
That doesn't make any sense. Lowering prices may increase consumption, but it reduces profit margins, it doesn't increase profit margins. It may increase overall profit, but historically it's been the opposite - high oil prices = high oil company gross profits.
Never mind that while our largest export is gasoline - our exports of gasoline are still completely dwarfed by the amount of oil we import. To put this in perspective, we current have a net export about 500M barrels of refined petroleum products/day. We import about 9000M barrels of oil/day. In other words - if we stopped exporting gasoline, we'd simply lower our oil imports by about 5%. That'd be nice - but still a LONG way to go before we get close to net-zero oil imports.
Regarding gasoline exports - the main reason there are record exports is because some refineries are at very low utilization levels - oil refineries are selling refined products to keep utilization high and attempt to remain profitable.
Margins on refining operations are extremely low. Most of the cost of a gallon of gas/diesel is the cost of crude oil. If you can't keep refinery utilization high, you will lose money if you can't increase prices because of the fixed overhead cost of running a refinery.
That's the primary reason 2-3 east coast refineries are looking to be sold off - their utilization rate is in the low 60% rate - while refineries along the Gulf of Mexico and midwest are in the 90%+ rate thanks to the influx of cheap oil from shale production.
These refineries in the GOM and midwest are making great profits because of the WTI / Brent crude spot price spread. The GOM/midwest refineries are paying about 10% less for crude - the east coast refineries are forced to reduce their margins to compete and in fact they are not able to.