Why Russia moved away from 650 mm submarine torpedo tubes

Why did Russia apparently abandon 650 mm torpedo tubes on its submarines?

Smaller torpedoes became good enough, while the large weapons cost more and consumed magazine space that could hold a greater number of standard rounds.

The proposed explanation is that improved weapons for smaller tubes made the larger torpedo unnecessary. A 650 mm weapon takes up more internal space and brings additional cost. Smaller weapons can therefore allow more torpedoes in the same-size hull. The benefit depends on the smaller torpedo already being adequate for the job, rather than on tube diameter alone.