Why cant QE2 be written like this QE11?

The offical line from Cunard is that Queen Elizabeth 2 is named after the first Queen Elizabeth ship - hence the Arabic rather than roman 2.

However it is thought that she was meant to be named simply 'Queen Elizabeth' and it was the Queen who accidentally added 'the second' during the naming ceremony. This caused a problem because QE2 was built in Scotland, where the Queen is only the FIRST queen by that name - the 2 is thought to be a compromise to avoid causing a problem in Scotland.