At a guess, there's a limited number of free radio bands that the keyfobs can use , making clashes likely.
The rx/tx chipsets are going to be the cheapest available , so likely the same in both keys.
The 'codes' are ultimately only numbers of fixed length and without international standards, duplication is easily possible
Most of the above is still true for metal keys, except you don6 normally try them in other people's locks.