Why there are no adjectives(-ed form)for intransitive verbs, for example, words like happened (It was happened), occurred (It was occurred), etc, While transitive verbs having the adjectives ending with "ed"?
The constructions with adjectives that were originally participles of verbs are very closely related to the passive voice construction. And the passive voice construction, in turn, is only possible for transitive verbs.
As CGEL says (p. 1436),
There is a large-scale overlap between adjectives and the past participle forms of verbs, and since the verb be can take complements headed by either of these categories we find a significant resemblance, and often an ambiguity, between a verbal passive and a complex-intransitive clause containing an adjectival passive as predicative complement. Compare:
 i The kitchen window was broken by the thieves. [verbal: be-passive]
ii They were very worried. [adjectival: complex intransitive]
iii They were married. [ambiguous]
Broken in [i] is a verb, worried in [ii] is an adjective, while married in [iii] can be either. The ambiguity of [iii] is very clear: in the verbal interpretation it is dynamic, describing an event, while in the adjectival interpretation it is static, describing the state resulting from some prior event. Compare They were married last week in London (verbal) and Hardly anyone knew that they were married - that they had been for over ten years (adjectival). We will see, however, that this sharp semantic distinction does not apply in all cases.
Adjectival passives are passive only in a derivative sense, and we will not say that[32ii-iii] in their statal interpretations are passive clauses: they belong to the complex-intransitive construction. The term adjectival passive applies only to the predictive complement, that is, to the AdjPs [adjective phrases] very worried and married. Thus the clause They were very worried is not itself an adjectival passive - it merely contains one. Passives in the strict sense are always verbal;41 more specifically, we restrict the term be-passive to clauses like [i] or [iii] in its dynamic interpretation, i.e. to clauses in which be is a catenative verb taking a bare verbal passive as complement.
41Adjectival passives are sometimes called 'pseudo-passives', though this term is more widely used for prepositional passives.
Having said this, many intransitive verbs allow prepositional passives, and in some cases it is possible to form adjectives that come from those. For example, from the prepositional passive
This problem has been talked about.
we get the following adjective:
This is a talked-about problem.
Example of usage in published literature:
corruption was the world's most talked-about problem
From Paul M. Heywood, Routledge Handbook of Political Corruption (2014) (link)