OpenTTD sadly does not simulate passengers as unique agents. Transportation demand can be very unidirectional and not make logical sense.
Personally this isn't really a negative. I've found that I only care about "agents" when the scale of the game focuses on caring about individual units. Once you get beyond that, I don't think the simulation necessarily is more interesting just because it uses unique agents. And conversely, I've never thought while playing SC4 or similar game that "This game would be better if it simulated all citizens as unique units".
A number of games simulates unique agents: Tropico, Rollercoaster Tycoon, Theme Hospital, Two Point Hospital, Ceasar 3 / Cleopatra etc. etc.
Its a different game entirely compared to games like Sim City or City Skylines. I've noticed that these "individual agents" games are very "unstable". They're only designed for a limited number of agents before everything goes to crap.
As such, "individual agent" games tend to be scenarios that you play for a short time, rather than trying to play for months on the same map (like Sim City or City Skylines or OpenTTD can be).
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Tropico Boom/Busts grow too variable and uncontrollable. You'll eventually have an island-wide boom/bust collapse that probably triggers the instant-loss endgame (aka: Soviets and/or USA invades).
Ceasar 3 / Cleopatra are reasonably stable, but definitely a smaller map and designed for scenario play instead.
Personally this isn't really a negative. I've found that I only care about "agents" when the scale of the game focuses on caring about individual units. Once you get beyond that, I don't think the simulation necessarily is more interesting just because it uses unique agents. And conversely, I've never thought while playing SC4 or similar game that "This game would be better if it simulated all citizens as unique units".