Yes there may be no limit, but it also means you have no stock of the high demand A2, aptamil products.
There is a limit by virtue of having no stock to sell. Easy to say we'll sell you unlimited A2 but say yeah but we have no stock.
Why do you think daigous drive all over Sydney to just pick up two tins at a time? Must be fun
Also the nirvana you describe, once daigou shopping becomes too easy, then there goes the profits for the daigou. It's only profitable because of the 2 tin limit and the time it takes to gather so many tins.