If you take it from the roots of yoga, which I have been told is to facilitate meditation, that's the point.
You get distracted, your mind wanders, you feel uncomfortable, but you stay there and try to bring your mind back - you return to focus on the sensation of your breath, the feel of the mat against your back, the way your limbs feel from the asanas, you notice the sound of the bloke at the front as though he's about to start snoring, you bring your mind back to your breath again, maybe how it feels for your lungs to expand, you think about the washing up waiting at home, hear the sounds of somebody getting up to leave early and bring your mind back to yourself again.
You're learning that these distractions dissipate when you refocus. The irritations pass, as do all things. Your heart rate slows because for ten minutes, you stop and just be. The things that would have you raging, you turn away from them in your mind, they have no hold on you. You've turned away from the outside world and its stresses through activity and action, now you are turning away through your mind.
I'm not sure if that makes as much sense on the screen as it does in my head - but I learned through yoga and meditation not so focused on getting 'a great figure', initially to try a new way to deal with chronic pain. The thought of staying still for a long time was scary, I associated it with more pain, so I'd resist, tense up and feel stressed, which meant more pain - but going through the discomfort and learning to observe the discomfort then move my mind onto something else really helped.
And then I had one meditation session where I was going to partly escape from the general shit show of my existence, but as I sat there, trying to focus on my breath and failing utterly, I felt the deepest, most crushing sense of loss and sadness - but I stayed still so as not to disturb the others. I couldn't run away from the feelings, so I had to experience them in their entirety. But within five minutes, the emotionally pain started fading as I became aware of the sunlight warm on my shoulder, then the scent of the floral arrangement to the side, then back to the air on my lips and I felt the most amazing sense of peace for the last few minutes before the session ended and I slowly got up, put the zafu and blanket away and wobbled off home.
A 'pinch the physical bits from the practise without an understanding of the psychological or spiritual principles behind it' class doesn't give you that. Because it allows you to run away from uncomfortable feelings, rather than experience them. I certainly didn't gain enlightenment from those meditation and yoga classes, but I did experience something that changed me and gave me the ability to feel calm rather than scared with stillness and less critical of my body whilst more aware of it. Which isn't a bad thing in my opinion.
It's handy when I'm at rep 8 of a tough set in the gym in making sure I don't give up when I absolutely could complete the last two reps - and indispensable when my internal dialogue is screaming at all and sundry (or one particularly irksome person who is incurring my unspoken wrath because they're being demanding when 50 other tasks are also requiring my immediate attention) and I need to remain both vaguely competent and ultimately, employed. 😇