Lots of countries managed to hold exams, don't know why ours didn't.
Hindsight is a great thing.
We had no idea what was going to happen at that point. Numbers could have gotten out of hand. We didn't know hw many students and invigilators, and school staff would have been ill and not available. Invigilators in particular are often older people, and often over 60s who are retired. In March we already had schools with reduced numbers for both pupils and staff.
The children were already missing chunks of time - the syllabus now means that there was probably at least a months worth of material to go through. Many courses still teach right up to the end, with lessons for students going up to May half term, even though exams have started. Coursework elements weren't complete. DD's final drama piece wasn't performed at that time as first the staff member was self isolating, and then 2 out of 5 students were.
If we'd had lots of staff and students off school ill or with symptoms its have become a big problem to sort. Any form of remote learning for the rest of the school would have most likely had to be stopped to cover exams in several rooms as it was.
There was never going to be the right solution and unfortunately what we have ended up with has been pretty much a disaster. But who was to know what would have happened if they'd tried to have exams - I know of a number of students and teachers who would have been ill or self isolating with symptoms over the exam period.