Every single wiki engine, and often even different sites using the same engine, use different TextFormattingRules. This is about making a “standard” for this, so that they can all use the same markup.
There have been many attempts at creating WikiMarkupStandard:
This would involve creating a detailed specification that would cover every and all relatively common aspect of wiki markup. Then all the wiki engines would have to implement, and all the wiki sites convert to using it. This is fairy impossible to do.
The WikiCreole markup has a number of converters and plugins for various engines, but it’s still not widely used on many wikis.
Different wikis have different needs, and require different markup to easily cover them.
Different wiki engine developers and admins have different tastes in what is “good markup”.
Inventing new markup (and a parser for it) is one of the fun parts of creating a wiki engine.