It's a problem in the US. The Galileo high accuracy service (HAS) is broadcast on 1278.75 MHz (the E6 signal). But the 1240 to 1300 MHz band is not allocated to satellite radionavigation in the US. It's allocated to radar with a secondary allocation for amateur radio.
Because of that allocation, the FCC cannot guarantee that Galileo HAS receivers will not be interfered with.
Galileo has like a dozen different signals and I believe that most of them aren't broadcasting yet. I'm not sure which of those signals is supposed to give 1cm accuracy, but it could be one of the encrypted signals. Another consideration is that the 1cm accuracy would only be possible with fancy DGPS or RTK setups. 1cm accuracy is doable with GPS today, but unless you're a farmer or land surveyor you probably don't own any hardware capable of realizing that accuracy.
I suspect this is an extremely naive question, but why would one signal give a 1cm accuracy and another one not? Shouldn't the satellite just tell you its trajectory + identification info so you can calculate where you are based on that? Or perhaps by signal do you mean the physical electromagnetic properties (frequency etc.) are unsuitable for high accuracy, rather than the actual information content it's supposed to carry?
To get good precision you need to remove the effect of electrons in the ionosphere. These basically change the index of refraction and therefore the propagation speed of the radio waves. The delayed signal makes your receiver think it is further away from the satellite than it actually is. One way to estimate this delay (instead of relying e.g. on the correction signal of a differential-GPS base station close to you) is to receive signals from the satellites at two different frequencies. The time delay is proportional to f^-2. Knowing the frequencies and the delay between the two signals allows you to estimate the electron content and and correct both signal to the undelayed "infinite frequency" arrival time.
orbits in space are geometrically perfect, you can reasonably talk about 1cm accuracy there.. On earth, variations in a long list of things, including physically moving land (due to seismic activity), make "1cm accuracy" something that does not actually hold.. no doubt it has a lot of positive measuring ability .. but the real truth gets messy..
Because of that allocation, the FCC cannot guarantee that Galileo HAS receivers will not be interfered with.
https://docs.fcc.gov/public/attachments/FCC-18-158A1.pdf