1. Psychological goals: it's more interesting to read "You probably don't need X" articles; they tend to have a bit of snark and humour and brevity to them which more straight-faced "Here's when to use X" don't. Bluntly, I'll read former even when I am nowhere near using X myself, as they may be fun and educational. I will not read the latter unless I'm closely involved with X, because they sound like instruction manual and world is full of those.
2. Target audience is implicitly different in the two titles - they are not interchangeable in my mind.
Assumption is that there is a far larger number of people who ARE using X but SHOULDN'T, and so the title/article "You probably don't need X" is written for them; than people who SHOULD be using X but AREN'T (for whom the latter title is more appropriate).
In all honesty, I've seen dozens if not hundreds of solo or small team startups/bootstrappers build a SPA they didn't need to and then fail, in part because they were moving to slowly.
"Here is when to use x" targets people who don't use x, but should, typically not the audience.
"You probably need y" targets people who might consider y, again not the audience.