More interesting would be the explanation of how such proteins and cell structures endured intact over the past 80 million years.
The article doesn't say those structures where intact, it doesn't give any indication of the level of decomposition of those structures. It is easy to figure out though how they may have survived. What causes decomposition? Exposure to air, microbes, light, etc. Absent those things, decomposition may stop or slow down. It is not an unknown scenario.
They didn't. If they had, they'd be petrified. Bone isn't the most porous stuff in the world, but it IS porous. There's absolutely no way in hell anything with soft tissue in it is millions of years old.