>>20547730Ash actually did in the second episode. He grabbed a bunch of strangers' Pokeballs in a Pokecenter to fight off Team Rocket since he didn't have any of his own yet.
As far as I can tell, the games have trading machines to justify having to go in a Pokecenter to trade and the anime decided to mimic the games. Now that they've been phased out of the games, I expect them to disappear from the anime as well and just quietly ignore trade evolutions.
>>20547229 pretty well covered what I had always made of the logic behind them, ie some bullshit excuse where the actual reason is that GF wants you to beg your friends to buy copies too.
Was there a time in the anime when people traded without a machine? I feel like there probably was. Hell, NPC trades in the games happen without machines too.