During the initial years of the 777 program, the 777-200ER was the most popular model. The 777-200LR was a niche market aircraft. It had more range then needed by most airlines. In terms of design, it actually has more in common with the 777-300ER than the 777-200ER.
Part of what made the 777-200LR unpopular is that its trip cost is almost identical to the 777-300ER, which can hold a lot more passengers. If you don't need the extreme range of the 777-200LR, you're better off getting the 777-300ER, which is why it has been vastly more popular with airlines.