You get a lot of flop from headangles that slack…
Less fork offset could help counter that.
My best guess, is that because it isn’t super slack and the bars are ‘only’ 750 wide, putting the longer stem on slows down the steering and makes me more confident to weight the front, so my body position shifts forwards a bit more and my arms have to reach forwards less far. But I could be totally wrong.
Yes… ish. More confident to weight the front? That’s down to the rider, as well as things like seat angle/reach, depending on whether sitting or standing. Wider bars increase the triangulation of the body over the bike, bringing it forward/lower; your weight will be further back with narrower bars due to the arms being closer together as they have to ‘reach less far’.
A shorter stem and longer wheelbase / slacker HA also means your weight has to move forward to maintain grip with the front wheel – it’s sticking out quite a way in front. It may be you were doing this anyway, or it could be you need to consciously think about doing it (I do).
Your hardtail’s angles will all also alter through the fork travel, pivoting round the back axle – something else to add to the equation.