Proteins do not degrade all by themselves. They are degraded by the environment. There are bacteria that eat it, oxygen that oxidizes it, water that gets into its nooks and crannies and unfolds it, and a whole slew of natural enzymes that cut it into pieces just because that’s what the body has to do to keep such junk from clogging everything.
Likewise, bones do not become hard and brittle just from age. Over time, as you use them, the body puts calcium in the bones to make them hard and brittle so they’ll be able to support your weight. The body doesn’t have any mechanism of stopping this process, so it just keeps turning your bones into limestone. If you die young, your bones will not calcify in the grave. This is why you normally find bones and teeth as fossils - they were already mineralized at the time of death.
Additional mineralization can replace soft tissue when it rots and mineral-rich water evaporates from the resulting cavity. If the soft tissue is completely enclosed by calcified bone in an airtight and watertight fashion, then it will not decay with time. There would be nothing in there to degrade it.
So no, it is not really surprizing to find soft tissue 65 million years old. It is rare merely because soft tissue is never fully enclosed. Even bone marrow has blood vessels going into it. To preserve it you’d have to have these holes plugged quickly after death, before the decay sets in. This does not occur often, making soft tissue finds very rare.
“...So no, it is not really surprizing to find soft tissue 65 million years old....”
How about a few thousand..?
Maybe if you reduced the temps to single degree Kelvin levels, otherwise the soft tissue should disappeared due to simple thermal degradation over 65 million years.