Egg Moves and Chain Breeding

[Zeofar]

You know, I was recently trying to figure out how egg moves work with the help of Bulbapedia and Veekun's Breeding Chain Finder. However, I am still quite perplexed by them. Would anyone mind explaining? Here is an example of the particular thing that got me confused again.
Sceptile, in the Dragon Egg Group, can learn Leaf Blade. Seviper is also in the Dragon Egg Group. Since Seviper cannot learn Leaf Blade in any other way, it is an Egg Move for Seviper, right? Veekun says no. And despite the Monster Egg Group which Sceptile is part also having members that are in Ground, Seviper nor any other Pokemon I have checked that are in the Ground Egg Group can seem to learn Leaf Blade. Almost every other move I have checked, even somewhat logical ones (A Zangoose with Crunch from a Shinx) are supposedly impossible according to Veekun. Am I missing a key element in the understanding of how Egg Moves work or what their limitations are?

 

[Shinx3000]

From my experience:

A Shinx can learn fire fang, ice fang and thunderfang from a granbull. They both have fangs, and can breed, so it can learn them.

Seviper cannot learn leaf blade because it does not have a blade like appendage on its body (is this game related or anime applied?) All the ones that can learn it have a blade thats a leaf on their body and gallade has blades on its hands.

And Certain Pokémon, like Magikarp and Beldum, cannot inherit any egg moves and start with only Splash and Take Down, respectively. Volt tackle cannot be bred onto a pokemon either from another, one pikachu/raichu must be holding light ball for a pichu to get it.

DOn't think that helped much, but I would like to know more on this too

 

[Amadeus Windfall]

The key element you are missing is that not all Pokémon can inherit any move from a parent, even if it would make some sense. Leaf Blade is not an Egg Move for Seviper - it cannot learn it in any way at all. The same goes for Zangoose and Crunch, and various other combinations. It would break the game if any Pokémon could inherit any move you could justify them using in any way - if you want to breed a move onto a Pokémon, you need to first check if it is an Egg or TM move they can learn.

Also, it makes perfect sense that Seviper cannot learn Leaf Blade - with the rather odd exception of Gallade, all of the Pokémon who learn it (Grovyle, Sceptile, Bellossom, Victreebel, Leafeon, and (as an Egg Move) Tropius) have leaves on their body, and the move's description says that "The foe is slashed with a sharp leaf." This shows that it isn't a move that uses a blade (like Seviper's tail), but rather that uses a leaf in a blade-like manner (again, excepting Gallade, who is sort of justified in that blades are something of a gimmick of his, having swords for hands and all).

 

[Zeofar]

I know that it doesn't make sense, I was trying a few logical things a while back before giving up. I tried this in an attempt to figure out what an egg move is, and I think you've answered my question. Basically, there are specific moves that Pokemon can learn, but only by breeding, and the only point of Chain Breeding is to get a single Pokemon with all the moves you want. Is that right?

 

[Amadeus Windfall]

Yeah, that's exactly it, with long breeding chains being for if none of the Pokémon that the one you're breeding can breed with can learn the move, but one can learn it as an Egg move from a Pokémon in another group. It's also useful for getting more out of your TMs.