Anglocom on translators' additions

As part of its excellent ongoing of tweets on French to English translation, the team at

Anglocom 

has raised a series of questions along the lines: Why did the translator add ... ?

The first tweet reads:

Some translators are in the bad habit of adding things that are not in the source text. If the FR says "gros," say "big," not "very big"!

This is followed by four examples:
(a) …ceux qui poursuivent son œuvre /…those who help carry on his work
(b) …les visiteurs viennent y découvrir… / …its many visitors discover…
(c) Surmonter les obstacles / Overcome substantial obstacles
(d) Elle a été davantage soulignée… / It received much more attention…

These tweets hit me with force for the simple reason — I have to come clean — that I am often guilty of precisely this. Such additions are common in my drafts and despite my efforts to delete them too many survive revision and rereading.

Why?
The only answer can suggest sounds very lame indeed. It's the nagging feeling that the English sounds either better or more familiar with the added word or notion.
And why might that be?
My first guess is that I, like my fellow offenders, are influenced by the English-language journalists we read. Is it poor style, fashion, or what? I have no idea. Certainly many articles by many journalists in both English and French can be improved by simply deleting unnecessary adjectives, adverbs, helper verbs and other excesses.

Two other contributing factors are time and talent.
Even talented writers need time to produce texts that are tight and crisp while others can't achieve 'tight and crisp' no matter how much time they have.
Does anyone out there know of any relevant academic research?

Comments very welcome indeed.