How come HM moves cant be forgotten?

Question

All other moves can be replaced by other ones. FYI I know about the move deleter, so dont put that in.

Answer 1

Game freak wanted to make sure that you can get out of an area and not get trapped in case you needed an hm to do so.

Hope this helps!

Comments

If you made a pokemon forget an HM and you need it to get out of where you are, you just teach that pokemon the HM again.

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In early generations of Pokémon this was not always possible.

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How come? You have the HM and you have the pokemon.

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One possible example is a Pokémon that didn’t learn the move through the actual HM but through other means. If you got to a location using that HM move, deleted it and didn’t actually have the HM to add it back, you’d be stuck without Fly. Plenty of HMs like Waterfall, Dive and others are level-up moves.
It would also be weird if you were able to delete Surf in the middle of use.

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In Gen 1&2, the timelord science that went into developing bags for Pokémon trainers was more primitive, and you had to be very selective about what you carried with you. This includes TMs and HMs, since they didn't have their own space in the bag until later.

Answer 2

Like most other things in Pokémon, this is one of those things that Game Freak decided to implement into Pokémon. You can't really argue with it.