What disqualifies のみならず from being acceptable in this sentence?


Below is a JLPT question that I'm struggling to understand

> ロボットと人間の違いは何であろうか。1970年代に盲導犬ロボットや介護ロボットの研究開発が盛んに行われたことがある。
> **しかしその当時は、技術レベルがまだ低かった○○、当事者たちに受け入れてもらうことはできなかった**
> 。目の不自由な人たちからは、「ロボットの研究者たちはわれわれの気持ちを理解していない」「われわれと心が通わない盲導犬ロボットの開発などはまったく意味がない」と非難された。また、病院の看護師さんからは、「ロボットには心がないからわれわれの代わりをすることはできない」ときめつけられたりもした。今ではロボットの技術も格段に進歩したし、医療、福祉に関する社会の助勢も変化した。しかし、基本的な問題が解決されたわけではない。生き物である盲導犬や看護師と人工物であるロボットとでは本質的な違いがあり、両者の間には超えがたい壁があるようである。

１．からこそ ２．だけあって ３．のみならず ４．こともあって

I understand why the answer is 4 but why is 3 not correct here? I asked a few
natives and they could only say that it was unnatural. I have some grasp on
the meaning of のみならず and have done some research beforehand but I can't settle
on any conclusive reason why it doesn't fit here, only that こともあって is better.
As the 2 clauses are stating facts it seems that it would be acceptable here,
but why not?




のみならず means “not only” and what follows it is expected to be some addition
that can be translated with “but also”. In this sentence, it would be another
problem that existed at the time in addition to technology not being advanced
enough. Robots not being accepted, however, seems more like a result of
technology not being advanced enough than an additional problem.

Let’s suppose, however, that those two can be connected with のみならず as two
problems, rather than a cause and a result, because that's not at all
impossible.

What makes the sentence unnatural in this case is the particle that marks
当事者たちに受け入れてもらうこと.

Since what comes after のみならず is an addiction to what is said before it,も works
well.

> 技術レベルがまだ低かったのみならず、当事者たちに受け入れてもらうこと **も** できなかった。

が is not bad, either.

> 技術レベルがまだ低かったのみならず、当事者たちに受け入れてもらうこと **が** できなかった。

However, は gives an impression that acceptance by people, which was not
achieved, is specifically focused in contrast to something that _was_
achieved, and this doesn't quite go well with のみならず.

This problem doesn't exist with こともあって because `ＡであることもあってＢ` states B is the
case, giving A as one of the reasons, and it is natural to put B in focus in
contrast to what was stated earlier or implied by context.

In `ＡであるのみならずＢ`, on the other hand, A and B are supposed to be an equal pair
and specific focus on B is not expected.




のみならず means “not only” and what follows it is expected to be some addition
that can be translated with “but also”. In this sentence, it would be another
problem that existed at the time in addition to technology not being advanced
enough. Robots not being accepted, however, seems more like a result of
technology not being advanced enough than an additional problem.

Let’s suppose, however, that those two can be connected with のみならず as two
problems, rather than a cause and a result, because that's not at all
impossible.

What makes the sentence unnatural in this case is the particle that marks
当事者たちに受け入れてもらうこと.

Since what comes after のみならず is an addiction to what is said before it,も works
well.

> 技術レベルがまだ低かったのみならず、当事者たちに受け入れてもらうこと **も** できなかった。

が is not bad, either.

> 技術レベルがまだ低かったのみならず、当事者たちに受け入れてもらうこと **が** できなかった。

However, は gives an impression that acceptance by people, which was not
achieved, is specifically focused in contrast to something that _was_
achieved, and this doesn't quite go well with のみならず.

This problem doesn't exist with こともあって because `ＡであることもあってＢ` states B is the
case, giving A as one of the reasons, and it is natural to put B in focus in
contrast to what was stated earlier or implied by context.

In `ＡであるのみならずＢ`, on the other hand, A and B are supposed to be an equal pair
and specific focus on B is not expected.

