I never understand people making their tree private. I know they get copied, but why does that matter? If you are confident your research is accurate, then it gets more credence as more people copy it.
Zaph
It is important to make 'quick and dirty' trees private precisely because they are created at speed with less regard for accuracy. Their job is to tackle a very precise question e.g. the identity of genetic forbears. It is correct that conventional trees should be far more accurately researched and as such we might be less concerned that they can be seen by others.
On your original question I tested with Ancestry in 2021 and since then have had hundreds of additional matches. I do not recall any of them contacting me until I'd contacted them. I currently have well over 20,000 matches on Ancestry and a similar number on My Heritage (albeit many are duplicates of Ancestry matches). On Ancestry only around 75 of my nearly 9,000 matches are at 40cM or higher and none are above 296cM. That means that the vast majority arithmetically are either very distant cousins or are false matches both of which reasons might explain partly why they don't bother contacting me. There are tables somewhere that show how many 4th cousins and more distant we might all have and it's a lot, which is why they are of less interest.
I am almost exclusively researching my paternal line and mostly my matches are from the USA whereas I am English which could persuade a lot of them that any link is false or weird or whatever. Yet another possible reason for lack of contact.
I also have one very good reason for lack of interest. I am not in my online tree because I do not know who my genetic father was, so anyone looking at my attached tree will only see my maternal side. Nevertheless roughly 40% of my matches are maternal and none of them contacted me until I I contacted them.
Maybe I am an unusual case but I do agree that the large number of matches who do not attach trees, or whose trees are limited to one of two 'private' names, suggests that a lot are only interested in ethnicity. That's their privilege, irksome as it may be to those of us with burning questions.
Tony