I think that one reason is that cameras back then were sold almost as inheritable items. People kept them forever and expected them to last forever. There was no constant upgrade cycle, so the purchase was seen as a photographic investment.
It's why many would engrave their cameras with identifying information, they never thought they's sell them. I see so many used/old cameras with the original owner's name/DL #, SS# on them!
W/re to SLRs, stuff like Nikkormats could be now bought for under $40. Yet they sold for about $800 back in the day. I bought a Nikon F3 in 1989 for $1000. That would be $2100 today. And yet I bought a perfect/like new one for $250 recently.