Shemittah is inextricably tied to the Land of Israel. Anything grown outside the Land, does not have the sanctity or restrictions of Shemittah produce. But what are the borders of the Land? I frequently see people posting maps of "the REAL borders of the Land of Israel" When I point out that their map is actually only wishful thinking, I quickly get un-friended. There are actually several "stages" of this question. First, there is the "Promised Land", vouchsafed to Abraham. This area goes far beyond anything we ever had, and is understood in the Talmud to mean what will be in the Messianic era. The second stage is called "the First Sanctification", and encompasses all the land that the Israelites conquered in the time of Joshua, right after the death of Moses. The term "First Sanctification" refers to the idea that besides the intrinsic holiness of the Land of Israel, it needed to be sanctified by a declaration of the Sanhedrin (Court) for the laws relating to Eretz Yisrael to be operative; including Shemittah. Lands added during the time of David and Solomon were also sanctified, but that sanctification was only valid while that land was held. After the Babylonians seized Judea, the Land lost this status of Sanctified for purposes of Shemittah, except for Jerusalem. When the Israelites returned in the time of Ezra, they re-sanctified the Land...as much as they held. This is called the Second Sanctification Exactly how much they held is a subject of debate. Most likely, it was the area around Jerusalem, sweeping down towards the coast, but not quite reaching it, plus most of the Galilee. The Second Sanctification is eternal, and therefore didn't end with the Roman destruction. Since we do not know exactly how far the borders of the Second Sanctification went, the entire Central and Northern parts of the country need to observe Shemittah, although there are parts that probably were not included by Ezra. Just to make it very clear, all parts of the Land of Israel are holy, but not all have the laws pertaining to the Land, including Shemittah.
The present day State of Israel contains areas with different statuses. Most of it is part of the Holy Land, conquered and sanctified by Joshua as well as Ezra.. There are many areas of the Holy Land that remain in Jordanian or Egyptian possession. There are, however, parts of the State of Israel which were never part of the Holy Land. This is true of the Southernmost part of the Negev desert (including Eilat), and probably some of the northeastern part of the country. (There is the minority view of Rav Saadia Gaon that all of the Negev is part of the Holy Land, but this is highly unlikely). Therefore, some people who are wary of all the previously mentioned methods choose to use only produce grown in these areas. This would be much too small an area to feed the entire country, let alone maintain an export industry, but is sufficient for those who wish to avoid the Shemittah restrictions without utilizing legal fictions.. On the other hand, they miss out on partaking of the sanctification of the Shemittah fruit, which the Torah declares holy. Some other people prefer to live on imported produce for the entire year.
What I have described here may seem picky to some people. But the goal of maintaining a balance between ideals and practicality, without doing violence to the Laws of G-d, are really what is at stake. Nothing could be more Jewish. May G-d open our eyes and hearts to His Torah!