Or … it wasn’t anywhere near as busy as it was made out to be.
If you are doing full on infection control (meaning basically no non emergency cases), and doing as much remotely then yes parts of hospitals are going to be basically shut down...
One of the reasons for this is there are hundreds of interlocking specialities in medicine, and if for example the specialists who deal with keeping patients unconscious or on ventilators are all moved to ICU or patients with covid it means that as an example you cannot do any routine operations because the people needed for them are already working full time, which might mean you've now got the medical staff who'd normally be dealing with those patients post op, often for weeks or months not doing their normal jobs.
Basically you take out planned operations because you need the staff and equipment for emergency/urgent care of one specific type and you suddenly end up with multiple recovery wards that are basically empty because there are no "incoming" patients for them, or an extremely reduced flow. You might also call off the major routine ops because a patient recovering from say a joint replacement is very vulnerable to infection and is far less likely to recover from say Covid than they mgiht have been if they hadn't just had what is effectively a major controlled injury to their body.
Add in things like the fact the lock downs IIRC massively reduced the number of urgent care requirements due to things like RTA's, and sporting injuries (one of the big things that helped the NHS cope with the covid patients) and the normal route from say A&E to pre-surgery ward, to surgery, to post surgery, to pre-release wards and care is now nearly empty so whilst in the average week a single operating theatre might be doing 10+ major operations and feeding those patients to aftercare in the hospital for a week or more each, now it's not happening so those wards are largely empty.
There there was the push to do as much as possible remotely, meaning that for example my brother in law's physio was largely done remotely (IIRC about 1 in 4 sessions was in person) via skype/zoom, and when he did go in for checkups/examinations of his arm it was very quiet but the physios were still working, they just were not visible and often working from home or different locations to their normal rooms (the location of which was determined by the fact that normally they had to be near each other because that was where the physio reception etc was*, something that didn't matter if they were working remotely).
then there is the fact that if you're in full on infection control mode, you are primarily treating emergency cases and trying not to have patients mingling, which means things like routine eye and ear specialists are going to have a lot of "spare" time because their specialities are such that you need them for emergency cases, but they're also not likely to be qualified to actually help much with say a patient on a ventilator (or no better qualified to help than a less specialised medic who certainly can't do the job in ophthalmology or audiology), and they can't do their jobs remotely.
*Going back about a year or so I had the funny thing with my father of going to a planned appointment for his hearing, going to the right department and the guy coming out and taking us to another area entirely because it housed some of the same equipment and IIRC the machine in his office was broken so he was using a "spare" that was in a related department when he needed it.