because it is not a competitor to any of the gambling sites as dice isn't a standard gambling game offered in fiat based sites.
If you are saying that they are chasing down "casinos" and not only dice sites then it is probably their intention but then again satoshibet hasnt close down their service to UK players , they couldn't possible slip out satoshibet. Also if you check on their letter that they sent to betmoose (references below)
Got a reply today:
You should note that section 33 of the Gambling Act 2005, which makes it a criminal offence to
provide facilities for gambling without an operating licence authorising that activity, applies if remote
gambling equipment is located in Great Britain, or if the facilities are capable of being used in Great
Britain. -snip-
Consequently, the fact that you do not have any hosting in the UK, do not market or advertise
to UK residents, and that your team do not reside in the UK, does not mean that a licence is not
required.
The first bolded part clearly indicates that means all form of "gambling" that a site offer and dice is one of them , also that PrimeDice is one of the biggest dice sites around so it cant be just slip away from their attention
The second bolded part clearly indicates that they are against every gambling sites without license which means they could / will take an action to all these unlicensed sites
All these indicates they are probably chasing down sportsbook only because most of their source of income comes from all these licensed sportsbook . So blocking all these unlicensed sportsbook will give them more income from tax as the sportsbook ethusiast will switch to a licensed sportsbook and thus generate more income to the sportsbook and more tax for the gambling commission