I can agree that if packs were smaller they might have less bugs and be easier to fix, but the main reason kits and stuff packs now have very few bugs is they don't introduce much in the way of new gameplay. They are mostly made up of objects with the same function as those in the game already (a new sofa or fridge, etc). That's one reason they are cheap (relatively; sort of a you get what you pay for) ; new animations take the longest to do. Some of the packs do have new items, but overall they are mostly just new in appearance.
I personally think that the reason everything moves so slow in the way of fixes is just the company's priorities. I know some bugs in the game might be hard to find, but the way the game has everything subdivided into individual xmls it shouldn't take that long to find a bug. Heck, they could just overwrite something that's not working and start from scratch. I mean, really? 100 people have left comments about weather inside houses and 190 have liked the opening comment. Yet they can't find it in five months? Or aren't sure if it should be fixed? Or just haven't found the time? I think there's been 7 patches in that time so plenty of chances to upload a fix.
But there have been 11, count them, 11 packs released starting in January of this year, and more on the way. There's money in new packs, none in fixing bugs (except to keep people happy, which has never been a priority). So what do you suppose most of the programmers are working on?