Backpacking is a culture that for some reason people take all too literally. Backpacking as a notion is more of the case of seeking out cheaper accommodation and being more versatile with your timeline in the interest of saving money.
A big part of it is also not having a certain itinerary and just kind of going with the flow. Rigid travel plans are not part of true backpacking and this is part of the tremendous fun! If you love it somewhere, stay until you no longer do. If you don't love it somewhere, leave earlier. This is real travel in my mind and it is also the best kind. There is just one aspect of backpacking that I think people, especially people new to the notion of backpacking, take all too literally.
And that is the backpack itself
I see it all the time when I am traveling. I encounter people in paved environments, loaded down like soldiers struggling to get down the road with their monstrous pack. Then later I will talk to many people, all of whom also have massive strappy backpacks only to discover that they have been to exactly zero places that aren't paved. They have not trekked for an hour to arrive a jungle homestay, they didn't even go to places with a crapload of stairs such as a cheaper mountain resort. There is almost no reason for them to have a backpack at all and backpacks have a lot of limitations.
The tube!
One of the worst aspects of a traditional backpack is that all of your gear needs to be loaded from the top or perhaps inside of the dozens of other zippers that line the backs and sides.
The reason behind this is pretty obvious and that is to assist in keeping your contents dry. The pack is waterproof but the zips are not and this is why there is only one access point, at the top, which has a waterproof cover as well. This is completely unnecessary for your average backpacker who isn't out in the wild braving thunderstorms on their bus journey from one beach to the next. In the meantime all of their belongings are crammed on top of one another and it is nigh on impossible to access the stuff on the bottom. Dirty and clean clothes intermingle and there is nothing worse than realizing you need something that is waaaaay down in the bottom.
They are heavy
When you pick up your 15kg pack the first time you might be thinking "oh this is no problem"... well it's gonna be. 15kg starts to feel like you are giving a child a piggyback ride after traipsing through city streets for many blocks or those long as hell corridors at the airport. This all could have been prevented if you had been a little more realistic about what sort of travel you are actually going to do.
And the solution is a more sensible rolling backpack hybrid.
See those zippers? See how they go all the way down the side like a regular suitcase would? Well that's going to make it MUCH easier to access your stuff than the "tube" like setup of a traditional backpack. See those wheels? That is going to make it much easier for you to drag your pack instead of piggybacking it... the wheels on these tend to be more robust than regular rolling suitcases, by the way.
And on the other side of the pack are shoulder straps just like you would expect a backpack to have. This will come in handy in the unlikely scenario that you actually have to go offroad for a bit.
let's be honest... most "backpackers" aren't really going that far off the beaten path, no matter how much they claim to the contrary. If you are that sort of person you do not need a traditional backpack. You probably are not going offroad because I have been backpacking for 15 years and other than Nepal, there were almost no situations where I truly needed a backpack at all.
Combine this with the fact that these hybrid backpacks are probably around the same price as the kind of backpacks that you will see "backpackers" all over the world wearing, and I can see no reason to bother with the old style.
Trust me on this one, you are going to end up regretting not listening to this advice after the first couple of days otherwise. These hybrid packs are gaining in popularity because the points that I stated above are absolutely true. Forget the image, forget the tradition, technology has come a long ways and we no longer need the camping backpacks for a majority of backpacking situations.