Reasons for the polysemization of "illocutionary act" (etc.)

Why did "speech act theorists" (authors such as Alston, Searle, Schiffer, Bach & Harnish) re-define the central terms of "speech act theory", such as "illocutionary act" and "speech act", so consistently, thereby making them more and more polysemic? The reasons, it seems, are at least twofold:

(a) From the beginning of "speech act theory", authors used, described and defined the term without being quite familiar with how Austin defines that term (after all, Austin had originally coined that term, and gave it is original meaning, which everyone using the term should certainly be familiar with, if not respect).

(b) Most authors seem to be unaware of the fact that you cannot re-define technical terms arbitrarily, just like that. After all, re-definition causes ambiguity, and ambiguity is, quite obviously, one of the most fatal faults a scholarly term can be subject to. So although there may perhaps be reasons strong enough to justify even the re-definition of a technical term, in the absence of such very strong reasons, re-definition of a technical term is a serious mistake.

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