It’s hard to create complex cell structures, for example, you can’t create insides of your cells cause the game fills it in automatically, external organelles (pilus, flagellum, etc) are placed outside of your cell, instead fill these areas with a darker toned cytoplasm that has no collision.
For weaker membrane types, this feature is discarded and inside areas are filled in, stronger membrane types will have this feature as an alternative to engulfing.
While typing this, I realized that you can make psuedo multi-cellular life with little constraints, another up to this idea.