Have to agree with OrlandoR. Reasonable or not, it is frustrating. I also agree the limit could easily be higher for day 1, I remember it being more like 250 in the past. The issue restricting feasible player numbers is more that medium-sized airports (or entire countries like NZ) aren't really viable when traffic is lower, ranges are shorter, and tech-stops are heavily penalised. But the bigger airports still support competition between ~6 airlines that normally turns into a couple of long-term successes.
But having a quick look around JA at the moment, the bigger airports have plenty of space for more players. LHR, AMS, HKG, ORY, IST all have just 3 airlines. Bangkok, Singapore, Toronto and Sydney only have 2. Beijing, Seoul & Cairo have just one each. Big airports in big countries that can support big airlines, like Manila in the Phillipines & Jakarta in Indonesia are completely empty. It's going to make things much easier for players in those airports, they now get to expand with minimal or no competition. If that's me, it makes things pretty boring.
It's more frustrating because this has turned out to be the first test of the very long game worlds, which is the thing that was going to get me back into playing AWS. But I've now missed the start, and while there might be slots open up in a week, there's no guarantee, and they'll likely be snapped up quickly. It might be a month before I manage to get one, by which time the game is 5+ years in. Can certainly still succeed at that point, but have to deal with limited airport choice, full order books, etc. Doable, but not as exciting as day 1 of a 64 year world.
Yeah, there are two other worlds I could join, but one is a more than halfway done MT, which doesn't interest me at all, and the other is BW, which I'm not really suitable for.
It's frustrating to see enough demand for another 50 spots on day one, enough airports available for another 50 players, but a game world that is closed to new entrants. It's more frustrating because I'm one of those who doesn't have a spot.