If the UK is that concerned, maybe they should just postpone this year's British Open. If the Delta variant is roaming around as they say it may be a good idea just to not have it. I don't see how the restrictions they speak of make it any safer.
One of the great frustrations of the pandemic is the inconsistencies in rules and restrictions that the various authorities (government or otherwise) put in place. Having the crowds at 80% at the same time as implementing some of these other rules certainly seems inconsistent.
As @DaveP043 points out, the situation in the UK is different from the situation here. I don't feel like I know enough about it to bash them too much.
Making the trip to The Open has always been something of a hassle for American golfers and the Covid just makes it more so. I wouldn't necessarily blame a player if he decided to stay home.
There are a number of places in the article that references government requirements. I took a quick look through Google, and see that the UK does still have significant restrictions on travelers, including proof of vaccination, testing, and quarantine in some situations. Those restrictions are going to apply to anyone visiting the country for the tournament. They are facing a surge in new cases, apparently associated with the Delta variant.
Given all that, its hard to blame the R&A if they're following current government guidelines and restrictions. And I honestly don't know whether the government policies are excessively restrictive, given the surge this spring from the Alpha variant, and the current surge from Delta. I'm just barely on the side saying the restrictions aren't too far, given the current situation in the UK.