There's value in in-person meetings that online classes aren't good at or simply can't provide so it becomes a trade off.
Cost isn't much of an issue. iOS developers tend to be paid well and even then it's often a reimbursed expense. I'm obviously not speaking for everyone here.
Most notably it's a means to network with other developers. One can recruit, find out more about other companies, meet the people working on their favorite open-source project, etc. Hands on technical support is significantly easier than doing it remotely, especially when external devices are involved.
Lastly, for many it's a chance to unwind and take a pseudo-vacation. The San Jose area has lots to do, there's plenty of evening events, and there's plenty of people who you'd have something in common with to socialize with.