'Cause it's more like sex education for the sake of him being able to procreate and show affection appropriately.
Humans may know how to fuck, but I can promise you most of them don't know how to make their partner feel good as well. Most of them don't even know where the clit is lol you also have to teach the importance of safe sex to humans.
So why is it suddenly weird just 'cause it's a monster being taught these things?
No, 'cause my brain isn't wired like a monster's. I'm human so using methods for humans ((sex ed videos, teachers and doctors explaining things)) would ultimately work if I had more than two brain cells. We don't need to watch two people bumping uglies to understand how safe sex works. We understand, or should understand, just by hearing what people have to say. It isn't the same for creatures who don't have the same thinking capabilities that we do. It's more like training a dog to do tricks than it is teaching a classroom of teens that you need to use a condom and birth control when you have sex to avoid babies and STDs/STIs.
Also, they expressed that the reason why Tako wasn't paying attention was due to his interests solely lying in Dr. Yu. They tried using videos of other people having sex, but Tako just basically did not care for the people involved. It was only suggested /after/ they had tried a different avenue that they should have sex to show Tako.
It's a series with monsters where the mc birthed a fleshy tentacle octopus monster. Why are you even trying to apply real world logic here in the first place??
Why do character like this always just go along with everything as if its super normal. Why are they having sex without 's second thought to show octo how to have sex? Besides the fact that he clearly already knows how to do it. Why do you go along with it so easily (╯°Д °)╯╧╧