Do you not understand that the supply (number of planes) is constant throughout the year, while the demand (number of fliers) fluctuates? If the supply enough planes for everyone to fly at peak times there’s going to be tooons of empty seats throughout the rest of the year. They’d then need to raise everyone’s ticket prices to pay for those extra empty planes, and people just aren’t willing to pay the extra price for the convenience.
Designing cities for transit is designing them properly. Designing them for only walking is a fairy tale thought up by a 12 year old with no real world experience. Look how well transit works in European and Asian cities. Vancouver is even halfway decent (tons of room to improve still).