If you don't travel from your house with it I understand your confusion, the weight is a factor when traveling. I never have back pain, but when I do, its because I'm carrying a heavy laptop around on my back.
Even around the house it makes a difference in my opinion. My 12” X1 Nano is much nicer to carry and use around the house than my 16” M1 Max MBP is, and so the Macbook spends most of its life docked. The MBP comes with me when I travel because it’s my primary computer, but reduced size and weight would be welcome. If only the 14” MBP didn’t sacrifice cooling capacity as much as it does.
I just schlepped 150 kg (in 30 kg chunks, and not 2km but some distance with lifting) and I’m entering my eighth decade on Earth. No back pain. Did have a little back pain in middle age, but a few years in the gym with a personal trainer fixed that right up. Fitness, my friend, fitness.
I travel with my laptop a lot, but much prefer a beefy workstation for all the work I do when I get where I'm going. The weight of the laptop is not a big deal, even my big Lenovo P53 (~30mm thick 15.6" black brick) is only 3 kg.
I do use an Osprey 22L hiking backpack for my daily driver, it's got a waist belt to transfer weight to my hips, a chest strap to keep the shoulder straps together, and internal semi-rigid frame... but that's more for all my other stuff, and for activities I do in the woods far from stuff like 'laptop computers'. Even if it's just in a handheld briefcase, 3 kg is not a lot. That's about as much as a water bottle - which I also have in the backpack, as well as a bunch of miscellaneous stuff that also weighs a few kg.
I herniated a disk a couple years ago due to a waterskiing accident, but I've fully recovered and even while dealing with that injury, walking around airports and so forth with any laptop is not not strenuous.
In hindsight, I wish I'd gone for the big P73, I miss the giant 17" screen of my old 40mm thick, 3.5 kg Dell Precision... but the OLED on the P53 is beautiful. 17" UHD OLED when, Lenovo?
Because they are laptops. I can't even use my 16" MacBook Pro on the couch. It's portable sure, but it's not a laptop. You can't take it anyway, only move it from desk to desk. It's the single heaviest thing in my bag when I travel.
I can do the same work on a MacBook Air when I'm away, and it's basically just a desktop when I'm home. To me it would make way more sense to have a desktop at home and a 12 - 14" laptop, if it wasn't for the cost of having both.
It's really nice to be able to take a laptop out and start working on an idea wherever you are. Macbook Air makes me more productive and home or anywhere because it's less of a hassle to boot up the laptop.
I have a gaming laptop, even 14", and I can't stand the boot up time and needing a thick power brick cable to get things going. I barely use it as a result and use my Steam Deck more.
Mostly, but also take it when I fly, along with a mouse + mouse pad. The weight has never bothered me, usually the backpack with the laptop in it is the lightest bag and then I have a much heavier carry on as well.
So that makes sense it is not issue for you if you mostly travel by car. But it can be for those that use bike or public transport or just walk. (As example last time I used car about two months ago).
When I'm walking around S.E. Asia and it's 90 degrees and humid I care about every extra gram.
Even an Air is too heavy IMO compared to say an LG Gram. But, I need the specs and the screen so I lug around a MacBook Pro 16" at 4.6lbs - often I have to lug around 2, my corp one and my personal one.
Given an iPad Pro 13" is 1.3lbs they "could" (for some definition of "could") make a 16" device with keyboard closer to 2 lbs.
Yes, I'd rather carry a lighter laptop, but that's mostly because of all the other stuff I want to carry in my backpack (eg groceries). If walking "a few kilometres with a 3kg gaming laptop on your back" is a problem for you, you're rather out of shape.
I have (at least) 2 laptops at any given time. They fit into 2 categories:
1) Is 99% of the time actually on my lap when I'm using it. It's (usually) the one I take with me when I leave the house. I care very, very much about its size and weight. It's an M1 Air and I wouldn't mind if it was a bit smaller/lighter.
2) Is 99% of the time sitting on my desk, plugged into my KVM. It almost never leaves my house. I don't care how bulky it is. However, I prefer medium-ish form factors in case I do need to travel with it.
Any laptops I have over 2 will usually be in the 2nd bin, but sometimes the 1st.
Only answering for myself here, but when I already have 10+ lbs of camera gear in my backpack, a huge gaming laptop makes a big difference compared to an ultrabook. And I'm not talking about an excessive amount of gear either. One body plus one lens plus a couple extra batteries, etc, easily gets me to 10 lbs. And then I still have to get on a plane with it.
Other than my work laptop (a horrible, horrible Dell Precision), my laptops hardly ever leave the house: MacBook Air M2, Lenonov X220 (Linux) and HP 17 (Windows). I still prefer the sleek and light one over the others.
I buy gaming laptops because they're the only powerful laptops and their size has never bothered me when traveling