5x5 and 3x5 are out of vogue for lots of reasons but it largely boils down to:
* Not enough volume
* Non-periodized
That first bit means different things at different phases of a lifting "career". But generally speaking "time under tension" and research into effective rep ranges has changed modern thinking on set sizes and volume.
These days people, including World's Strongest Men, tend to recommend higher rep ranges for beginners and those coming back to the gym to build work capacity and reduce risk of injury.