yes but the beauty is that, due to the lack of a central authority, the game theory of the situation virtually ensures that no one would ever do that — that is, take bitcoin2 seriously
I don't know if I agree with that. Like take the example of a country whose currency collapses due to government mismanagement and its people decide that they would be better off with a cryptocurrency. I'm not sure how realistic this is, but it's at least a scenario that I see proposed from time to time. Those citizens face a trade-off when deciding between Bitcoin and Bitcoin2. Bitcoin has a lot of active miners, which is valuable, as it means their future transactions will be more secure. But Bitcoin is also very expensive, and difficult to acquire. Joining the bitcoin economy is entering into a game where other players (bitcoin early adopters) have a huge head start, and these newcomers have nothing. If they instead start a new chain, they will need to bring their own compute power, but will have an opportunity to have a meaningful share of the tokens, and therefore some amount of influence on steering the currency.
It's probably unlikely that an enfranchised bitcoin user would be incentivized to jump to a newborn chain, but I don't think it's the case that a new user is always incentivized to adopt the existing chain. As the price of bitcoin increases, and the remaining coins to be issued decreases, a new chain becomes more attractive for new users.
Well Bitcoin does have almost central authority - if Top 3 mining pools decide to change their software in literally any way, then everyone else will comply of will be left in the dust. It's not that hard for 3 people to agree on a common action plan.
It's probably unlikely that an enfranchised bitcoin user would be incentivized to jump to a newborn chain, but I don't think it's the case that a new user is always incentivized to adopt the existing chain. As the price of bitcoin increases, and the remaining coins to be issued decreases, a new chain becomes more attractive for new users.