Strange the way Scientists can and are allowed to change the meaning of words to fit their very own beliefs, and you readily accept it as truth, fact.
THe meanings of words drift as their usage changes. Without digging into the semantic history of the word theory, I suspect that it is the colloquial usage of the word that shifted. Perhaps it was because a specialized term entered into general usage. I don't know.
I should note that in the law they talk about the "theory of the case" which is an explanatory framework that explains the evidence. The two sides of the case will typically have different theories of the case, but in each it (like a scientific theory) explains things. In the law case, a jury or judge will weigh the evidence and may need to evaluate how the two theories work and choose one as the best explanation.
Science is like this where sometimes new theories are generated to better explain the evidence (data) than earlier theories. Sometimes two theories will exist side-by-side, but usually one will be put aside in favor of the other. (or one will be consigned to a sub-set of situations where the simpler theory is still useful as is the case for Newtonian gravity and mechanics, relative to their relativistic replacements.)
Unfortunately, the colloquial usage in English of "theory" is as a a *speculative* explanation for certain facts or events. Typically these would never qualify as a legal or scientific theory.
Maybe we should make up new words every time we use a modified version of a concept in a new situation, but that's where context comes in. In a scientific arena or context, we mean "scientific theory" even if the first word is not stated.
[Aside: We should also note that the word evolution in general refers to "change with time" and can apply to many things. The unmodified word in a scientific context is take to be "biological evolution", though the astronomers are fond of referring to the changes in stars and galaxies as "stellar evolution" and "galactic evolution", though they don't use the word "evolution" just by itself.]