I suspect as a large American business they were concerned about being sued, basically.
Small businesses have responded rather differently. For instance my local Indian takeaway is operating totally as before with nothing changed whatsoever, whereas the chippy closed for a while and has now reopened with screens up, one person in at once and the staff looking rather like doctors in their attire.
I think there is a slight difference between smaller businesses, my local Indian , and Local Chinese for example are family run , so there is no need for social distancing in their kitchen , they all live together in the case of the Chinese they live above the shop . In the case of these smaller businesses it only needed measures in place to ensure customers practiced social distancing which in both cases have been done by only allowing limited customers into the shop and in the case of the Indian only allowing people to collect telephone orders or have food delivered .
But in a busy fast food environment like Mcdonalds , KFC etc there will be employees from several different households so there is a need for social distancing to be in place and fast food kitchens are not notoriously roomy setups , thats why the KFC outlets that have opened around here have done so with a limited menu and only for delivery or drive through orders , the same with the Mcdonalds that are scheduled to reopen .
Of course with both operations being mostly franchised I think it was necessary for the parent company to make a decision as well because otherwise it would have seen individual franchisees making decisions some of which could have resulted in brand damage . I think the right decision was to close for a period so modified operating practices could be brought into place .
I live in the USA and can totally relate. Perhaps to really open the economy we may have to change the law in the UK (and USA?) so that the threat of being sued is lifted. If we opened up only when totally safe(not realistic) that may help in not getting sued but as discussed in plenty upthread, the world economy and hence everything that follows from that could not handle it.
Im not particularly sure that we should remove the risk of being sued , I think the government should put clear guidelines in place and employers should then be able to rely on these . Be that the wearing of face coverings , keeping 2m away from one another . Giving employers immunity from legal recourse for their actions does not fill me with confidence that they will do the right thing . And could be used by some as an excuse to just take a cavelier attitude towards the health and safety of their employees . I mean look at certain examples of businesses like Sports direct that already have poor records when it comes to staff treatment and had to be forced to close their outlets when the stay at home advice was issued and shops of that kind ordered to close .