Why do learnsets change between evolution relatives?

I have been playing Pokemon since B/W but I am pretty new to the ins and outs of Pokemon. I was reading through the Pokemons learnsets and I was curious as to why certain Pokemon learn moves that the pre-evolution didn’t know.

For example, why does Stoutland learn Ice Fang, Fire Fang, and Thunder Fang at level 1 when its pre-evolutions cannot learn it? Stoutland evolves at level 32 so how can it be at any level below that? I know this is a stupid question but I have no idea why this is or how this is achieved. I searched but it only says this on Bulbapedia.

“Sometimes, Pokémon’s movelists vary between evolutionary relatives. This often is tied to a secondary type gained or lost on evolution, but can also provide incentive to prevent a Pokémon’s evolution to a higher stage.”

I am asking why this is and how it is achieved. Thank you very much

Pleaselog inorregisterto add a comment.

Some Pokemon can be caught in the wild with their level one moves, and there is also the move reminder who can teach Pokemon their level based moves in exchange for a heart scale… It is unknown why Gamefreak chose to do this gameplay mechanic, but probably to increase the challenge of Pokemon training.