Why would Stars remove this option specifically for UK players if not to comply with regulations? Removing this option will cost them money, because some UK players might rebuy or reload less often, and there is no upside in it for Stars at all.
Well I can make some guesses as to why. But that is what they have done - there is no new
gambling regulation in the UK that would have led them to do this. But there are new regulations coming in September. It's possible they are saying this change is to comply with the new requirements because to properly comply would cost more than the cost of doing this. Also - there is precedent for the GC changing their mind about policies based on player backlash so they might be hoping to create such a backlash again.
So possible upsides:
1. The cost of this decoy compliance is less than actual compliance.
2. Potentially pressure GC to change course on some new regulation by encouraging players to complain to GC to loosen planned rules.
3. To appear to be doing something in the spirit of the regulations as a means of creating a defence against enforcement action.
All 3 of these are exactly the kinds of behaviours that regulated businesses engage in all the time to avoid, limit or overturn regulations. Because the cost of doing so is less than the cost of full compliance.
There may be other factors at play. But for sure, they have implemented this and it is not based on a regulation. In fact the GC explicitly said this was not necessary in the past.