Let us be honest with ourselves. IF someone admits going to therapy, no matter how small an issue it was for or how far in the past it was, many many otherwise perfectly normal people WILL shun that person because of the fear of the unknown. That is a fact. The potential shidduch WILL be signifigantly reduced for such person.
Considering the above, why is it any shock that people don’t mention this, however it is justified. (It is minor; its like a toothache/headache/strep/etc.) And it may well be justified. Does the fact that you saw a physical health doctor any more or less necessary to mention to a shidduch (before first date; before serious; before engagement; or whatever point) than the fact that you saw a mental health doctor? Both types of doctor visits can be for a minot issue and may legitimately be no big deal to mention.