While encryption is of course just maths, governments have done a surprisingly effective job in the past controlling access to research and implementation. Granted this is significantly harder now with much wider proliferation of the internet. While this may not deter those with a technical interest much, it definitely does affect 'average users'.
As one concrete example, Netscape's SSL implementation was originally shipped in two versions - the 'secure' US version, and a severely compromised international download version, due to export controls on the encryption method used.
I'd also argue it's still not fully 'open' in the US - there's still a legal requirement to notify the government of any open source release of new cryptographic technologies, and some restrictions on distribution still exist. I also don't think it's a major stretch to imagine we are just one more San Bernadino style tragedy away from the first western government legislating to ban/compromise cellphone storage encryption, especially with the current US and UK political climates. One can only hope after San Bernadino that Apple has began preparing in earnest for that fight - I can't see any other big players having the moral conviction.
https://www.apache.org/dev/crypto.html
https://en.wikipedia.org/wiki/Crypto_Wars
https://en.wikipedia.org/wiki/Export_of_cryptography_from_th...