>>56402865>Draw your idea of how TMs workI can't into Paint or paper, but I can explain it.
To me, TMs/TRs work as CD/DVD files. You record the information about a move in a CD, and store it inside that tube case.
Now: if you want to teach you Pokémon that move, you put the Pokéball (minimized, of course) inside the little blue area. Then, you connect your Pokédex/PC/media outlet that allows you to see if your Pokémon is compatible with said move.
If it is, a small command will appear with your Pokémon's moves, and say "which move do you wish to replace?". Everything next is basically as gameplay: pick a move, he will forget this move for the one in memory, do you wish to proceed/stop?, etc.
If it isn't compatible, it will say: This Pokémon can't learn "X" move, please pick another one.
Now, the difference for me between TMs and HMs is that when you use a TM, the data in that disk is like RAM data: your machine finds it, and can pick it up, but is disposable and prone to corruption/deletion, so you better be sure to use it with someone you want.
HMs are more like ROM data: the disk will teach one move and one move alone. TMs are disposable data, something somebody recorded once. But HMs are more like permanent commands, so they are more secure to use. Move Deleters are necessary because they have more specialized equipment to make your Pokémon forget that command.
As for TMs after Gen 6, well, a lot of one use CDs leave A LOT of plastic, and we know how crazy people is with "muh ecology" and "muh recycling". Besides, someone probably picked up people who knew how to save TMs/TRs may as well be scammers because if you need many same moves, they can charge you full price, so is a negative net gain for (you) AND a plus for them.