I'm 6'5". To be clear I do always try for an extra legroom seat unless it's like 1 or maybe 2 hours tops. I don't go out of my way to pick jetBlue, so the "everyone gets legroom" thing isn't a real competitive advantage. I just consolidate my flying with a carrier and with even the lowest status tiers you generally get free extra legroom seating. Not giving everyone extra legroom seats means they can lower the sticker price and reward frequent fliers. The short people don't get nearly as much benefit from the extra leg room and don't value the seat as much so higher density means lower prices for everyone.
When I didn't have status I just paid for it, but every seat having extra legroom isn't in and of itself enough to move the needle for me.