Why are foods often packaged in weird measurements?

Quite often, it's because a manufacturer prefers to decrease the size of a packet than to increase its price. Customers notice when the price goes up but don't tend to notice the product getting smaller.

For example, jam in the UK used to be sold in jars containing one pound, which became the equivalent 454 grams with metrication. But, more recently, that's shrunk to 400g and even 350g in some cases. Similarly, according to Wikipedia, Yorkie bars used to be 70g, which then became 64.5g, 61g, 55g and now 46g; packets of crisps that used to be 30g are now often 27g (10% smaller) or even less.

While 127 is a weird number, 227 isn't - it's the grams equivalent of half a pound. In most cases where something is a weird (nonround) size in metric measurements, it's 10 fluid ounces or a quarter of a pound or something else reasonable in imperial units. Why so many 454g packages instead of 500? So the same machine can be used to make 1 lb packages (just need different labels) for the US market.

The one thing that's not been mentioned: the size of the package needs to be something easily shipped. A standard pallet in the U.S. is 48" by 40" (not sure about Europe, but I'm sure they have a similar standard). While boxes can overhang the 40" side a bit, it shouldn't be by more than a few inches, and they certainly shouldn't overhang the 48" side, or the forklift/pallet jack won't be able to operate safely.

Say your food came in boxes 20" by 10" by 4" - so you can fit say 8 on a pallet row. This is a chocolate bar, say 4" by 2.5" by 0.5", which works out to 4oz. So you can fit 5 deep 4 across and 8 high- total of 160 bars per case. Great.

Now you want to shrink the bar by around 25% (so to around 3 oz). But a 3" by 2.5" by 0.5" bar now won't fit neatly in a 20" by 10" box - you'd have 2" extra the long way. That's bad news all around. So you make it 4" by 2" by 0.5", which fits nicely (5 deep 5 across 8 high, 200 boxes/case), but isn't quite a 25% reduction in volume per bar - so it's now 3.2oz. Well, okay, make it 0.4" high - okay, now 5x5x10 or 250 per case, fantastic, a bit more than 25% reduction though, now it's 2.56oz...

Of course you could switch box sizes, but in some case you can't really do that - either because the company is a smaller company with a more limited box size choice (and perhaps a ton of pre-printed customized boxes they don't want to toss), or because of some other restrictions. Very large items particularly have this problem. As such, sometimes sizes are chosen for volume-to-ship criteria rather than just round-number-on-box.

This will not be a direct answer to your question, but bear with me.

When a producer is choosing their packaging, they have several options. They can portion by weight or volume (or amount, but that's useful less often for produce). They can then choose whatever serving "size" they want; producers of new products may have to determine sizes by themselves, but most often there are already standardized or normalized packages out there. Either way, though, these sizes are based on a combination of how much we - the consumers - are the most comfortable with buying, but also based on average consumption. This means that different products have different preferred sizes.

Added to this, different countries use different measurements (e.g. the US's imperial system or regional trends like dozens) and, finally, what's to say that 127 g is any more random than, say, 100 g?

100% marketing

When the packaged weight serves no normal recipe use, or is not a round number e.g. 1 Kg

When the price end in .99 or .95

You are a victim of marketing

Avoid these if you can, or just smile and carry on