I am always puzzled by the holiday ads for dishes and gravy boats and casseroles and such. Dave was cooking some chicken tonight and I admonished him to use cooking spray. We discussed the casserole dish he was using. I said I was pretty sure it was a wedding or shower gift. Which would make it almost 50 years old. Do people not keep their stuff? Do they buy new stuff every couple years? I don‘t get it. I‘ve used the same cookware for 50 years.
To answer the question in bold: Keep in mind there are always younger generations coming up, establishing their own 'households' both as single folks and as couples. So some things there will always be a market for because even if you figure older generations had an average of 2 kids--some of them had more. (My folks had 4, a paternal Aunt had 6) so even if they wanted 'heirlooms' which they may not, most families probably wouldn't have enough basic household items for all.
Then there's simple accidental breakage and catastrophic losses to fire, flood, tornadoes. When i was 8 we had a house fire that claimed all personal, household and workshop tools (the fire even leaped 4 ft from house and burned/melted tires off my bicycle) as well as books and linen, crocheted and tatted items that had come over from Hungary with my Grandmother as a teen bride. However items are broken or destroyed some will need replacing.
That said i have decorative crocheted potholders (in the shape of doll dresses and Christmas colors) that my Maternal Grandmother gifted my Mom after my parents divorce. i also have have oval shaped corning ware and still working Hamilton Beach drink mixer that probably hails from the 1950s that was also my Dad's. Oh, and a long decorative only plate/bowl (you know those soup/stew bowls that were as big around as dinner plates but had a shallow bowl shape--allowed quicker cooling and had wide rim to rest bread/rolls on?) It came from Hungary with my Maternal Grandma as part of a set, at some point it was a cracked 'survivor' of many moves and became my Moms when G'ma lived with her. When my mother died one of my Auntie's tried to claim it, but the Eldest (and my favorite) Aunt said 'No, that's the Esther plate, it is hers (pointing at me) and some day will be hers (pointing at my then not quite 2 year old daughter. My daughter is actually 5th generation Esther.
And i have books i've had for 60 yrs or more. Some gifts, some things i bought with babysitting money when in my early teens.