They do not decrease.
In general, it is impractical to de-allocate memory.
For example, now the vector can shrink and then grow again. It would be unnecessary to free up additional memory (and copy all the elements in memory), only to redistribute it later.
If the vector is compressed, there is also a good chance that the vector will be reduced to empty and then destroyed. In this case, the release from compression loss will also be a waste of time.
It can also be a useful optimization for reusing a vector object to avoid highlighting / placing content. This would be destroyed by the introduction of exemption, as it is being reduced.
In principle, most of the time freeing up additional memory is not worth it. In those few cases where this is possible, you can specifically ask about the transaction.
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