That's just farmed blueberries. Wild blueberries are smaller, with blue and much more flavourful insides. It's an unfortunate reality with grocery stores that since people buy based on looks, farms will optimize for what looks good rather than what tastes good.
Maximum size and number of berries are determined by variety, and largely trade off against each other, though (probably climate dependent) some varieties just don't seem to do well at all.
Actual size and sweetness is determined by how much water you give them and how long you leave them on the bush. Optimal picking time is determined by: go down and see when you think they're ready, then wait 2 more weeks before actually picking them; there should be just a handful starting to go bad. With some (but not all) varieties, you can also go by feel: if barely touching the berry makes it fall off, it's ready.
If you only have a small number of bushes and they aren't fully enclosed, the birds will eat them all before they actually ripen. At commercial scale this isn't very significant since the area can't support that many birds for the rest of the summer.
with wine grapes, sweetness (and other flavor qualities) depend on the sunlight times ratio of surface area of leaves to number of "berries". If the weather is great, you can grow more great grapes, but if the weather is poor you prune off half the fruit when it is still small and green (it's called the green harvest), and the remaining grapes come out higher quality, concentrating the sugar from more leaves.
You might try it with a blueberry bush to see if those fruits taste better.
No, it's a different species, vaccinium corymbosum. It's farmed, because it can be farmed, because of the bush size and growing conditions.
Wild European blueberries, vaccinium myrtillus, can't be farmed. If we could, we would, but we can't, so instead we employ hordes of seasonal workers to go out in the forests and harvest them during the month-long season.
If you remove all the excess water from farmed blueberries, the taste is about the same. You just need to aggressively sweat them.
This obviously doesn’t work if you want to eat them fresh, but there are better berries for eating fresh anyway.
Larger blueberries weigh more and so there is selective pressure and growing preferences which lead to large watery tasteless but heavy berries as the preference for crop outcomes.
It's all about ROI.