With lesbians this may happen faster than with heterosexual couples and I have several half-baked theories as to why this is so.
In part, lesbians are so good at figuring out what our partners want, and giving to them, that it becomes a bit of a drill, a hell of a lot faster than some poor guy trying to figure out what the hell is going on down there. By the time he gets it, his wife has already been frustrated for years, and is grateful for anything even remotely resembling what she might actually want!
The point is to not always just give each other an orgasm as quickly and efficiently as possible, so you can go to sleep, but to enjoy the process of getting there, and getting there isn't always the most important aspect of love making either.
Another reason for the speedy demise of romance among lesbians, may be their penchant for collecting cats. The bed becomes laden with cats (dogs, ferrets, parakeets, peeves and resentments), making sex close to impossible without disturbing something.
Setting personal boundaries is another area in which lesbians do not excel. Being joined at the hip constantly, even during bathroom time, can kill a romance faster than a bare foot jackrabbit on a red hot skillet in the middle of August. The nurturing of mystery is crucial to the survival of the libido.
It has also been my experience that a good many lesbians, deviants that we are, lack an adventurous spirit or creativity when it comes to sex. Many of us are too shy or embarrassed to even talk to our partners about things we'd like to experiment with, or have even done in the past, if we feel our current partners might not approve. The inability to communicate our needs for fear of being judged harshly pretty much insures that those needs, those unspoken, secret, dirty, hidden needs...will not be met.
Am I suggesting that we fumble around a lot so that things stay "interesting" for a longer period of time? Not exactly... Of course if you wish to ensure this so called "lesbian bed death" go here and follow these steps.