That's what's fashionable today (or yesterday? I can't keep up), but it hasn't always been the case.
For the last 20 years I have been doing this it was the case. Before that too.
So not sure what you are referring to.
You sure you are not confusing campaign sites with actual digital tools and resources? It's never been a trend by designers to want to overcomplicate the design. The strive for whitespace runs so deep in most designers that you simple don't get the used car salesman mentality where every little pixel left untouched is one to much.
It's entirely possible my experience was atypical, the I did a lot of reading about UX at the time and this seems to be what the "best practice" was at the time.
So if a dialog was shown the best way to do it was to have the dialog expand from the clicked element for instance. Now dialog's are frowned upon.
What you are talking about is product people or product owners not designers.