With a ruler, there is no reason to assume each inch is consistently the same. We can find that out. I did that, and I am no scientist.
You cannot do that with the past, because you assume constant rates, and so on, but have no way of verifying that everything was constant.
You can therefore put any supposition to make it work for what you observe. Then say the supposition is true.
Take cosmic inflation for example.
Cosmic Inflation Theory Faces Challenges
Is The Inflationary Universe A Scientific Theory? Not Anymore
Decades of claiming something is true, and using... your famous words, "We know...", tends to give an impression that "we know everything". When in reality, you don't really know, but sad to say, many find it hard to say, 'we believe'.
However, that's what it is.
The only time it comes out, in public, is after the belief has been demonstrated to be wrong. Then you see in writing, "scientists believed", or "scientists assumed".
The next morning, you will hear, "We know...". When the only thing they know is that what they thought they knew, they did not know.
Will you admit that you don't know, but you believe?
I doubt it.