I think some of the opinions expressed above are a bit naive, and/or reflect inexperience with legacy EDP systems (that's what they were once called). Having ancient data in deep archive storage is relatively inexpensive -- making it as available as the current data can get very expensive.

Why pick on United? Every financial institution I deal with as a consumer limits how far back you can query transaction history (not even close to what's suggested), and that's what we're talking about here, as each flight segment would be considered a transaction in a database (or file system). Putting aside the mergers and changes of system platforms, to expect that you could readily query 30+ year-old data (dating back to the beginning of Mileage+) borders on the realm of silliness.

And, given that a significant number of us are in tech and software, how many have actually sat in a design meeting or seen a requirements document where it was stated that data must be easily retrievable 30 years on? Other than Social Security, which had the concept of a long earnings history from its inception, I don't recall seeing published and/or queryable consumer-oriented history that shows more than a few years.

In your personal life, are those 8-track tapes still working for you?