I think that's a subjective view, especially considering that many players don't have a strong understanding of English. This makes the quest to obtain the bike much more difficult for them due to the Language barrier. Regarding your point about the lack of forums or guides in the past, we have to remember that life moved at a slower pace back then. Comparing Pokémon from around 20 years ago to today's version isn't quite fair. If you consider various psychological aspects and how people have changed, the differences become clear.
Around 20 years ago, a 10-15 year old kid playing Pokémon would likely enjoy exploring, reading, and aimlessly hunting or battling in the wild without worrying about the time spent. There weren't many other games competing with Pokémon, aside from games like Zelda and certainly nothing comparable like Pokemon itself. It had a monopoly in its era, so if you liked the game, you had to find your own way without guides, videos, or forums. That was part of the charm back then, and most of us LOVED that part back in the times. But as comfort has increased over time, fewer and fewer people enjoy exploring or facing challenges. They tend to choose easier options when things become uncomfortable, like asking for help (Pokedollars) in Vermilion City.
However, times have changed, and diving deeper into this would just take us off-topic.
As you mentioned, "it's a Pokémon game", and the primary goals are to complete the story, catch Pokémon, earn money, and engage in PvP or PvE.
uhm, what do you mean by "but obviously not for 20k?" could you give an alternative then and explain why ?
the current price is 40k (if we exclude the Ditto). When players typically reach the point of buying a bike, they usually have around 20k.
Doubling that amount means they would have to double the number of NPC battles and every other activity to afford it.
I think 20k is a fair and balanced price since it's roughly the average net worth of a player when reaching that stage of the game.
Basically, they are exchanging almost everything they have for the increase of mobility.
In my opinion, 30k would still be too much, as it represents a 50% increase over their net worth at that point. So in my opinion 20k seems optimal (bhimoso 2nd suggestion), and adding the requirement of catching a Ditto would be a nice extra challenge.