Because in Russia they sell not apartments, but square meters. Accordingly, in the pursuit of profit, developers have increased beyond a reasonable width of the buildings. The facade for lighting the room is small, but the depth of the apartments is gigantic. In order to somehow adapt unlit spaces, architects began to come up with utility rooms, built-in dressing rooms, etc.
Do you mean that the dimensions of the premises have become almost the same?
One of the versions is engineering and technological.
It can be assumed that it is easier for architects to calculate the supporting structures of buildings, and for builders to erect them ... Less hassle with slabs of different sizes, formwork, etc.
There is also a market-economic version.
When calculating the cost of an apartment, the total area is taken into account, i.e. price of a square. All other things being equal, the buyer is interested in a larger living space, which means, if possible, he will buy a more expensive apartment.
However, it would be worth asking the builders about this, but for some reason they are in no hurry to answer.