Simple Explanation
The easy answer is 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.
Latin never had a *readatio noun, and thus neither does English. It did, however, have lectiones that were read by lectors. The word lection does exist in English, but it is by no means common, especially today. Few would understand you outside certain ecclesiastical circles. From the OED:
1885 W. Pater Marius the Epicurean II. 135
Those lections, or sacred readings, which..occurred at certain intervals amid the silence of the assembly.1927 Alan Hugh McNeile An introduction to the study of the New Testament 383
It [sc. the Codex Bezae] contains certain lection marks which Brightman holds to be Byzantine.
Technical Explanation
In their professional linguistics paper on “Restricting suffix combinations in English and German” from pp. 451–490 of the journal Natural Language & Linguistic Theory, Vol. 20, № 3 (August 2002), authors Mark Aronoff and Nanna Fuhrhop write:
Although English morphology has a highly productive Latinate component, the fact that only the Germanic suffixes obey the monosuffix constraint shows that the two types of suffixes are still distinct. Furthermore, although Latinate suffixes may disobey the constraint, they attach to unsuffixed words much less commonly than Germanic suffixes do, and they normally attach to suffixes which also carry the feature Latinate, so the picture drawn here is that there are two different word-formation systems, especially within the combination of suffixes, one Germanic and one Latinate. Latinate suffixes do not attach frequently to free monomorphemic stems, while Germanic suffixes, for the most part, do (this is the monosuffix constraint). Latinate suffixes attach frequently to free polymorphemic stems, while Germanic suffixes (except ‑ness) do not. So, the two types of suffixes are largely in complementary distribution.
The major takeaways from that paragraph that apply to your question are:
- English has two distinct word-formation systems.
- Latinate suffixes seldom attach to free monomorphemic stems,...
- ... least of all to ones that themselves lack the Latinate property.
Your verb read is a a free monomorphemic stem which furthermore lacks the trait of being Latinate, while your various ‑tion/‑sion/-cion type suffixes are Latinate ones.
Hence the constraint against that combination.