The lighter your baggage is the more mobile you are, you can go easier further to have more accommodation options, more transportation options, good luck carring your suitcase on unpaved road, mountain, forest or just broken sidewalks or high curbs every 10 meters.
Now I travel with my family each summer for beach vacation in Europe, we still pack each person only one small backpack - after all what you need for hot weather in Europe for ~10 days? Bunch of t-shirts (let's say 1 per 2-3 days of vacation, you can rotate them), shorts/dress (if girl), underwear, swimsuit, sandals, flipflops (wear sneakers into plane, they take the most space) and just in case of bad weather light jacket and one long pants, kids are even able to put there plush toy, book, some drawing tools. This summer we just bought sun umbrella for like 8EUR which paid itself in one day compared to renting sun umbrella/berth, though we were unsucessful in selling it, so it was not for free, but we didn't need to lug it with large suitcase as some people. When the kids were small (unable to carry their own backpacks) I could pack all 3 of us into one 50L backpack with wife having her own 24L backpack.
I don't really understand travelling for summer vacation with large suitcase, what are people packing there, are the moving or what? I am always astounded when kids are going to school trip for FOUR nights, they leave Monday morning and Friday noon they are back, yet parents pack these kids large more than 50cm tall suitcases full of things, my kids with one 24L rolltop backpack (rolled down) and smaller (half empty) 15-20L daypack are always kids with smallest baggage, yet they are not missing anything, now I started to pack even towel and 50ml shampoo/shower gel since they have some crappy accommodations not providing it.
There are record 35-40C temperatures in Europe this summer, yet now when they went to camp for one week I saw again all the kids with large suitcases for hot weather, what the heck are ALL these parents packing. Out of 60 kids there was literally ONE other kid which had like 50-60L large backpack, everyone else medium/big suitcases and their accommodation provides shelves to store your things, so they don't need to live out of suitcase which is the only benefit of suitcase over backpack (though there are duffel bags you can wear as backpack).