Somebody has to write the standards. Transit agencies don't care about making a data format that works for other transit agencies, as it doesn't affect them. Only companies that need data from multiple transit agencies will do this kind of work.
There are two approaches to aggregating data. You can either treat each agency as a unique snowflake, or you can convince all agencies to use the same format. The former approach means that all work you do is only for you, and you've built up an interesting base of intellectual property in an industry that doesn't matter. (There is no money in providing transit directions.) The latter means that anyone can show up and do neat things with transit data. (I have my own little webpage, jrock.us/mta.html that uses this data to provide me with exactly the interface I want. Do you think the MTA wanted to hire programmers to make this for people like me? Absolutely not. But they did make it for Google, and now I benefit.)
