That does seem rather extreme, especially as there are many tasteful professional outfits that should not be tucked in (and conversely, many outfits unsuitable for the office that
can be tucked in).
Hey, what if you're pregnant? Most maternity tops that I've seen don't get tucked in...
Now that I think about it, I suspect that the Catholic school I attended had a strict dress code for teachers and staff. Obviously, we students had to wear uniforms

, but I can't recall seeing a teacher wearing anything other than a suit or dress (or a habit for the nuns), except for P.E.
The same wasn't true of the public schools; teachers often showed up in jeans! There was a dress code, but it was almost never enforced.