That LM design was still evolving
The illustration showed an earlier design of the LM with two docking ports, one on top and another in front. It was decided that the front port wasn't needed and was too heavy, so they converted it to a door for the lunar walks. There was a lot of discussion about only using the top port because of the difficulty of approaching the CM while looking up. If you go to Episode 4 of "From the Earth to the Moon" (Spider), they discuss this issue. That and the Apollo 12 episodes are my favorites in the series.