@deprecated_ii could be that it has to deal with more things at once with more fights, more passengers, etc. If they haven't upgraded the hardware then it's obviously that and not the software. If they have updated everything but the software itself, then the likely culprit is that the OS has had enough changes that stop supporting it. I mean, Windows had some change in the last year that killed my capture card completely because the devs don't make drivers for it anymore. Similar breaking changes happen everywhere. Enough of those over time could make a program start to crawl. There are games like that too, where you need to drop in mods or old files in order for the thing to even work or run at a playable framerate.

Of course, not updating the system is obviously a security risk so it isn't like you can just not update it.

Who knows, it could also just be that the software was always like this but people's expectation of how it should operate has changed.