Many did assume a worldwide flood. It is worth noting that the 47 or so KJV translators did not have access to anything approaching our range of lexicographic and syntactical tools today and they all came from a relatively narrow academic background (by modern standards.) Of course, they had no training in modern linguistics and there is limited evidence that they regularly consulted Jewish rabbinical scholarship. And even they depended a great deal on the generally accepted traditions of the time, incorporating in countless contexts almost verbatim the wording of previous translations. They were also heavily influenced by the Latin Vulgate. And King James I (aka James VI) and the Church of England hierarchy also had their influence.
As to the “modern imposition” of a world-wide flood interpretation, nobody to my knowledge claims that what we are describing is an exclusively modern phenomenon. Indeed, it is based on a tradition with roots going back centuries and which has been more and more reinforced by various cultures and linguistic factors.
By the way, just to mention a technical linguistic point, the era of the 1611 KJV Bible was within the early phase of Modern English. This was also an era in which the idea of a spherical earth (i.e., “the globe”) had made huge inroads into the general non-academic population. Well educated people had known of a “global earth” for many centuries, but Ferdinand Magellan’s circumnavigation of the globe in 1522 was a feat the average person could grasp (even though it seemed absolutely incredible to imagine completing such a voyage.) So the English word earth was heading towards a much wider semantic domain, one that the growth of public education systems would influence considerably.
Many did and do. And I’ve watched English Bible translations improve greatly even in my own lifetime.
You can see these improvements when comparing translations on one of the many multi-Bible websites. However, you can’t always see the associated translation footnotes. Most translators consider the alternate translation footnotes at the bottom of the page an essential part of the Bible translation. Translation is never a 100% equivalency process so readers should not ignore them. Moreover, some Bible publishers and translation sponsors who are worried about alienating tradition-bound readers and potential-buyers of their translation sometimes put pressure on Bible translation committees to choose wordings which are more traditional, even if they are somewhat ambiguous or even misleading to some laypersons. Bible translators are typically contract laborers and may have limited say over the final product—although the General Editors and the Bible society, if involved, often but not always have veto power over the publisher. [This is a big topic and there are many Bible versions, so I can’t address all of those publisher relationships in one sentence.]
Most would argue that the alternate translation footnotes at the bottom of the page help protect the reader from most false impressions. (I’m generalizing but this is a huge topic because not only are the linguistic issues complicated but text critical issues pertaining to variant manuscripts also arise.)
The translations which render ERETZ as “earth” rather than “land” in those early chapters of Genesis are not wrong per se. The word “earth” is a valid translation. It is simply more prone to misunderstanding by readers. Even so, reader misunderstanding can and will happen with virtually any text on any subject.
It is also important to recognize that a Bible translation is not meant to solve all interpretation issues. Bible commentaries, study Bibles, and even paraphrases provide additional information for the lay reader. And these are also among the reasons that well-educated pastors study Greek and Hebrew exegesis in seminaries and graduate schools. Most complex topics are confusing to at least some degree until one dives into an academic program or intensive self-study. That happens regularly with science topics on Peaceful Science where the specialists have to explain where the average non-scientists (or some scientist outside of the associated specialty) gets things wrong.
When I was fresh out of graduate school, I could have pontificated on this topic in reasonable detail. Nowadays, especially in retirement when I don’t keep up with the scholarship, I would have to defer to better minds.