To be fair, I think allowing flights a year in advance is probably far more complicated than just updating the underlying date format. Even if they were able to solve that problem, airlines probably can't easily operationally plan that far ahead due to so many moving parts, i.e. committing to routes and schedules, planning for staffing that far ahead of time, ever changing government restrictions, fuel price fluctuations, inflation, geopolitical realities, staffing, etc. I mean, imagine if they did, and something like COVID comes along again, it would cause far, far more disruption if they had booked out the next few years in advance (we had no idea how long COVID restrictions would last while we were in the heat of it, it's only clearer now in retrospect).

Also speaking as a software engineer myself, it's almost never just a software fix that will magically solve everybody else's problems, that always ends up being just wishful thinking