My wife is from a large family. When her mother died in 1991 about 2,500 people, only about 120 of whom I knew, walked through the line to shake hands, and offer their condolences.
Her dad died in 2013, and since he was 88-years old, I didn't expect many to come through, and only about 1,200 came to the wake.
Both times some of my in-laws in the reception line came down with various illnesses in the day or two afterward. I knew they were infected by people who did not adequately wash hands, or breathed on them for too long.These were pre-COVID-19 events.
Through experience, we have a good idea how disease spreads easily among people close together who are hugging, shaking hands, or breathing on each other. At times close contact cannot be avoided, and as much as I try to avoid COVID-19, I have had it 2x, and I know how I got it each time, and it wasn't through hugging or shaking hands, but people breathing in the same room less than 6-feet apart. So far I have been lucky -- it has had very little effect on me. But, I worry about my 88 and 89 year old parents.