The answer is quite simply because *read* is a Germanic verb, whereas all those others come from Latin verbs and indeed often enough from actual Latin nouns like English *conjugation* < [Latin *conjugatio*](https://en.wiktionary.org/wiki/conjugatio#Latin).

Latin never had a **readatio* noun, and thus neither does English. It did, however, have [*lectiones*](https://en.wiktionary.org/wiki/lectio#Latin) that were read by [*lectors*](https://en.wiktionary.org/wiki/lector#Latin).