It's different schools of tthought and even usage IMHO. Also a matter of trends.
There was a time when extras were what brands offered supposedly because people wanted them. Ever more elaborate back adjustment systems, side pockets that expand yet still allow for those open side pockets for trekking pilots, various versions of cords to hold trekking poles on your front straps or to the side but very readily accessible, etc. All weight crept up until there was a 4kg+ behemoth of a sack.
Then lightweight movement came. People were getting lighter and less bulky kit. They started asking why do I need a 90 litre top capacity? Why do I need those side pockets when I'm only putting in my water bottles and open pockets can take that with less material and weight? Why do I need that lower region access when I'm only top loading anyway? Plus a thousand other questions. Brands started asking them too not least because they were seeing lightweight brands coming from people's garages to fill that need.
But go back to say the 70s and early 80s. Front cover of "The Great Outdoors" magazine (before initialisation) had a picture of a guy doing a winter Munro round. What did he carry? A 1kg karrimor tent for one thing, a sack weighing something around a kilo, etc. He used mainstream kit but it was real quality designed by people who actually used the stuff to their extreme. Climbers, distance backpackers, etc.
Basically we were light and simple then went heavy and feature laden. Now we really can get what we want if we really know what we want. It takes experience and poor choices to get there.
For my backpacking a single compartment main body, no side pockets (climber sack style), a large top pocket, open side pockets with side compression straps and a weight from 600g to 1.6kg depending on the needs for my trip. My summer base weight is sub 6kg for backpacking, possibly about 4-5kg. That's low bulk so 32 litre running sack weighing sub kilo will do for short summer trips in the uk. Longer UK trips I use a 59 litre climbing sack with 15 litre overload capacity. That can carry 28kg and be as bearable as such high weight can be. It was that weight that caused me to go lightweight.
That sack is 1.1kg and from the 90s. Yes it was against the grain in terms of weight at that time but there was a market for alpinism where you hit the big routes carrying less kit to enable you to complete it quickly without needing that big carry. A few brands quietly offered the kit for it. Mine was berghaus but it could have been Lowe Alpine or crux or lightwave I think came from the end of that era too.
For me a long back, basic climbing sack with no side pockets and simple but very effective load transfer and strap adjustment. As I said, my berghaus sack has a special side strap that pulls the sack into your back. It's designed for allowing climbing with that loaded sack. It makes it as stable as a light daysack even when carrying 20+kg.
