If it makes you feel any better, if this weren't an expat forum and you had just said, 'I'm going to the store to get saltines, yum yum!' I'd still have said the same thing (because there are many cracker varieties in the US too). I've always found them a bit crap.
You may be detecting some hostility because these seem like somewhat pointless and disparaging questions. You're pointing out rather petty differences and asking, in a way that implies inferiority of the UK, why things aren't like they are in the good old US of A. Why does there have to be a why? As cheesebiscuit says, different countries are just different and have different things and there doesn't need to be a reason. We could ask why the US doesn't have brown sauce or Heinz baked beans or Galaxy chocolate, but it would be just as meaningless. Those things aren't there because they aren't. You can find them in particular places, like you can find saltines here, but they aren't widespread and that's just how it is.
You may say that you don't intend any disparagement with your questions, but if you read them again, they all have a UK-negative element about them, and the title of your post also implies that these are inferiorities for which you must have an explanation. I'm not saying you can't miss things from home (I go to great lengths to get Brasilian food and drink items, so I do understand) or ask if/where you can find them, but if you do it in such a way that makes people feel like your subtext is, 'Why does this stupid place not have any good stuff in it?' you might find people getting a bit huffy.