If the pages remain inactive for a while, the'll become unloaded/suspended.
I think that the entity to blame, is the authors of said pages that make it impossible to bookmark for later consumption. That's the sad thing with www of today. Unpredictable and unreliable. Free pages that become paywall after certain amount of minutes/views, generated pages that changes information, broken bookmarking and so on
"That is 278 wasted tabs. 278 wasted processes. 278 times I broke my focus for no reason."