That's a cultural thing. Tokyo Disneyland, for example, has the majority of its customers and CM's arrive and depart via the busy Maihama station about a 10 minute walk from the front gates of the parks. But that's also why Tokyo Disneyland closes up shop promptly at 10pm even on busy days, without an extra "convenience shopping hour" on Main Street USA - they have to get all the CM"s out of there by the time the last train leaves for the night at Midnight. It's also why if you stay at the ultra-expensive Tokyo Disneyland Hotel or MiraCosta at DisneySea your sole perk is "Early Entry" of exactly 15 minutes before park opening each morning. That's all the time they can spare for Early Entry because the CM's can't get there any earlier than the first train of the day. Seriously - 15 Minutes!
Tokyo Disney Resort is fabulous, but it's daily operation is hindered by the constraints of trying to operate at the whims of Tokyo's public transit system. It's unlike anything you'd have to deal with in the American parks, because most American CM's drive their own cars to work.
As for Anaheim, there is a big swanky train station just down Katella Avenue from Disneyland.
Anaheim's station has over 50 trains per day stopping there; 24 Amtrak Surfliners north and southbound, and another couple dozen Metrolink commuter trains serving both the Los Angeles line and the Inland Empire line. .
Anaheim Regional Transportation Intermodal Center (ARTIC)
A free shuttle bus (funded entirely by Orange County sales tax) sits out front of the big station waiting to take anyone arriving or departing via train directly to the front gates of Disneyland. But very, very few people take that option even though the shuttle bus is free, the trains are fast and furious, and the Anaheim station is convenient and gleaming with shops and cocktail bars and restaurants inside.
Your Free Shuttle System To Disneyland Compliments of Orange County taxpayers - Usually Empty and Unused.
Americans just don't naturally take the train to vacation spots, or for their weekend entertainment plans. They prefer to drive their car, which is often faster, cheaper, and easier than a train even with some freeway traffic.
It's fun to be free!