This isn't something unique to crypto, it is universal market economics.
In the real world, USD basically functions like btc.
It is the the cornerstone from which most other economies base themselves on.
When a country with a weak economy peggs their currency to the USD, it allows room for economic stability and growth.
Yes, they then intrinsically tie their monetary value to the us economy, but stability is the result.
There have been numerous cases where a currency has depegged itself and allowed its currency to free float.
The result is hyper inflation and economic recession.
The same thing will happen if these cryptos were allowed to "float"
but not all stablecoins are centralized. take ampleforth for example: https://www.ampleforth.org/
they even got a security audit recently - https://www.ccn.com/ampleforth-stablecoin-improves-security-after-audit/