Because the entire concept of robot babies being actually conceived is incredibly hilarious and hilariously incredible.
***
Leela: It's okay, Bender. No one here will laugh at you for not knowing where robot babies come from.
[The other teen robots in the room, contrary to what Leela said, actually do laugh but then hang their heads and sigh.]
Tinny Tim: We don't know, either.
Farsworth: [holding a videocasette labelled "ROBOT SEX ED: DIRECTOR'S CUT"] Then prepare to be embarrassed.
[Farnsworth puts the tape in the VCR. The TV turns on.]
Narrator: [reading title screen] SEX ED. VOLUME ONE or PANTS FULL of SHAME!
[Cut to: A teen robot walking on a sidewalk]
Narrator: Meet Gerald, a maturing young robot.
Spotty Teen Robot: Hey, he looks like me!
Narrator: His hideous appearance is a byproduct of his hardware gearing up for an important mission: reproduction.
Fat-bot: Oh boy oh boy oh boy!
Narrator: Since factories can't manufacture enough robots to meet demand, robots can also reproduce by mating.
Bender: Aw, now you tell me!
Narrator: First, Gerald must find a female robot. The best he can do is Francine.
[Cut to a fembot, who buzzes.]
Narrator: After beer and hot wings at a local gas station, the two enjoy intimate time behind a dumpster. It's all perfectly natural. Let's watch, aroused, as Gerald's antenna uploads a binary file to Francine's internal drive.
[A series of ones and zeros become sperm and go into a hard drive.]
Narrator: Manufacturing specs from each parent are then merged by a randomized algorithm and the resulting code guides assembly of a new robot. [Gerald and Francine's baby blows a raspberry.] Yes, everything your body does is perfectly natural.
[The spotty teen robot and Fat-bot high five each other.]
Narrator: Except masturbation! That's...just...wrong!!!
[The teen robots hang their heads in shame.]
[Title Screen: THE END]
[The TV turns off.]
Bender: Daaaw, I can't believe I made a kid! I'm not ready! There's so much in the world I haven't stolen yet!
Leela: Relax, Bender. No one would let you near a child. Bev will get custody and you'll be a deadbeat dad who never even bothers to know his own son.
Bender: [wiping a tear away] You really think so?
Leela: I know so. You're absolutely horrible in every way.
Bender: [still sobbing] You're sweet, Leela.
***
http://www.animeflavor.com/index.php?q=node/27967