As an Ex staff member who actively tried to enforce these rules i know just the answer.
Issue being that rules such as naming cons, mixing (mostly mixing) will go unpunished because staff are not enforcing it because its not 'too severe' by the admission of US staff team about 3 months ago. If you do try to enforce these rules you will be bullied and your day will be made 100 times worse by people who just hold grudges because you told them that mixing is against rules.
From experience i can tell you that my mental health extremely tanked as soon as a bunch of idiots started harrasing me all over the internet from CN (I couldn't prove it was them since alts but it was kinda obvious). If you ask, yes you can mute them, ban them and whatever but if they follow you afterwards, it doesen't really matter, which then inturn leads you to not enforce certain rules even subcontiously. Also that there are biases involved, majority of US players know one another and will try to cover for them (in the rarer cases, but can still happen).
To summarize this. US is much more combat oriented, you will find mixing and generally its unfriendly towards roleplay unlike UK.
Another example of this would be someone telling a person who is A-1 to change their name (from just codename) because they are not on A-1 job. On UK this is absolutely normal, but on US.. good luck not getting burned at the gates by the community.
Even on UK you won't usually be warned for Nam.Con if you fail to remove your name on roles that aren't CL4/regiments with perms, only if you're clearly taking the piss.
I think this thread is partly blown out of proportion, but I will add my own addenda
-Casual racism on US In the D-block. Usually hearing the N word and/or hard R. Staff are aware of this issue and haven't increased punishments for severe toxicity to discourage it. Has been an issue for multiple years and a failure of US's SL part.
-Casual RDM, toxicity RDM, etc. Far more common to be killed over grudges that aren't explainable in-character. Usually, the other guy just gets verbal'd on US. On UK, you're looking at a warn minimum, and a guaranteed ban if he used a slur and you get it clipped.
+Overpolicing on UK. Much like the 'real UK' (we all know the UK isn't real, much like new zealand) - Mods are far more eager to dish out punishments. I don't think this is a bad thing, so long as you stay in the rules, but it can lead to some headache-inducing appeals and/or tickets where you have to spend 30+ minutes discussing why you did osmething
+Far stricter rules on combatatives, and what they can, and cannot do on the UK (When I played US literally nobody got in trouble for using 22415 as a combatative, not the 22415 instance OR the combatative telling them to do it). Majorly hampers gameplay but encourages a far more roleplay environment where usually you're kidnapped instead of shot if you don't have a gun out. (Thaumos can't BTFO people anyway but it was a huge issue for a bit)
Both servers have their flaws, but US is literally what MRP used to be, and it's awful to see.
Atleast on MRP we had people who were actually funny.