because vectors are not designed for that. When they mean "dynamic" they literally just mean ontiguous memory, removing the first element would leave an empty space at the beginning. To maintain contiguity, all other elements would need to be shifted one position forward. This operation is linear in time complexity
O(n), as it depends on the number of elements in the vector.
Also Vectors manage their own memory allocation and deallocation. If the begin pointer is incremented without moving the elements, the vector would still be holding onto memory that it's not actually using for storage of active elements. This can lead to inefficient memory usage.
Basically speaking: they are designed to modify the end, keep adding, take a bit off, split them at a point, but not really take away from the beginning ( and I mean literally the first element)
Also Vectors manage their own memory allocation and deallocation. If the begin pointer is incremented without moving the elements, the vector would still be holding onto memory that it's not actually using for storage of active elements. This can lead to inefficient memory usage. Basically speaking: they are designed to modify the end, keep adding, take a bit off, split them at a point, but not really take away from the beginning ( and I mean literally the first element)