The most likely (i.e. without reading the source and finding out) answer is: because it wasn’t that obvious.
You don’t understand the nature of bugs, in general, if you think that was necessarily “obvious” - the only guarantee is that it was obvious only for YOU on YOUR machine.
A fair question is why does the engine allow bugs of that nature to happen in final release without being noticed on other machines, but that’s a much more complex problem; it may simply be that they have too little determinism in their backend systems.
OTOH, sims-online has a testing system that should have had a 99% chance of detecting this bug, so … either they’re not using it, or you’re a one-in-a-million case. I would guess the former.
Finally … EA doesn’t give a flying f*** in a thunderstorm what you think: you are one in a million customers, and that they have a million customers is more important than that 100% of them are happy. This is merely basic economics; you may hate it, but in a capitalist society, it’s exactly the right thing to do.