I searched the difference between von Neumann and Harvard architecture and came to conclusion, that comparing to Harward architecture von Neumann has no positive sides, only negative such as "bottleneck" and vulnerability. So why most computers use von Neumann architecture today?
With a Harvard architecture, the ratio of memory allocated for instructions vs. data is determined by hardware. Once the chip is made, you cannot adjust the ratio. Allowing both to reside in the same memory is far more flexible. This flexibility is important since modern computers (and even microprocessors for embedded devices) are designed to be able to perform a wide variety of tasks.
Modern processors maintain separate instruction and data caches on the processor die as well, giving you the best of both worlds.