USD is a currency which many people can relate to and and are aware of its current value (more or less) with respect to their own local currency.
I cannot imagine a Panamenian knowing the exact balboa equivalent to a rubel, lol
Besides in a day to day live they operate in USD already.
Same Egypt, when you deal with anyone as a tourist, they would operate and calculate is USD.
When people talk about Bitcoin price, they usually refer to its price expressed in dollars. I really don't understand why...
US Dollar is going down in price, US economy is collapsing. There are many other countries which has more Bitcoin users, like Russia, China, Japan, Philippines and the whole Eurozone. Even ICOs are forbidden in the USA. It's not a so Bitcoin-friendly country, its national currency is not so strong. So why price Bitcoin in $?
There could be many other more appropriate currencies like EUR, CNY or RUB...