It wasn't not done by all, or even a majority, and I don't think it lasted long. It seems to have been countermanded in April. Still not good, but short-lived, if so.
"The Queen’s Nursing Institute (QNI) – the world’s oldest nursing charity – discovered one in 10 care home staff surveyed was ordered to change DNR plans without discussion with family members, nursing staff, or with the residents themselves." which does imply that 90% were not.
and "One anonymous respondent, when asked about DNRs, said: “We were advised to have them in place for all residents. We acted in accordance with medical advice and resident wishes, not as advised by a directive to put in place for all by a Clinical Care Group representative. We challenged this as unethical." so it could be and was challenged.
That some care homes went ahead is deplorable, but it is also reported that "At the beginning of April NHS England medical director Stephen Powis wrote to NHS staff banning the use of blanket DNR forms after discovering a Port Talbot practice had asked elderly patients to complete forms to stop emergency services being called if they contracted Covid-19.* (my bold type) so it does sound as though whatever instruction was send out was rescinded.
That is why I asked (before I read the news items) whether it was a temporary thing or permanent, whether it was still the case.
Resuscitation of the old when seriously affected by any illness at any time is something that has pros and cons, and is a difficult decision to make.