In war, the movement of things is everything - not just for armies which march on their stomachs, but for the economies of the countries that fight them. This is particularly true of the world today, where raw resources (e.g. iron and peaches) may be shipped many thousands of kilometres before they are made into things (steel and peach-gloop) which can be used in other things (tinned peaches) which can well be shipped right back to where those raw resources came from in the first place (iron mines and peach-plantations). Disrupting the flow of trade and supplies is a valuable war goal because it can weaken an enemy's military forces and economy, but stopping the flow completely is the ideal - and that's what blockades are for.
This invites the question: why a naval blockade, given that there are other means of supply and trade - rail, road, and air? The simple answer is that the vast bulk of supply and trade, especially over long distances, is conducted by shipping because the sea remains the most cost-effective means of transporting large volumes of goods. This was triply true before the 19th century as there were no aeroplanes, motor-cars, or locomotives - shipping was the only means of supplying substantial forces or maintaining high volumes of trade, even over short distances. Despite that, before the 19th century the world economy was overwhelmingly agricultural and even the smallest and most urban countries (e.g. The Dutch Republic) also had primarily agricultural economies. This meant that there wasn't much trade over long or short distances, relative to today, and most of the goods that were traded (sugar, spices, tea, clothes, tools, fish) were not essential to the continued well-being of the economy as a whole. Moreover, if this flow of trade were stopped then many of these goods could just be sourced locally. That said, many early-modern countries made most of their money from taxing trade - so even though a blockade wouldn't necessarily hurt their economy, it would hurt their government's coffers.
At the same time, the trope specifically uses the naval blockade, as the definition of a blockade does not require it to be sea-based since you can blockade landlocked areas as well with ground units (such as what the Soviets did to West Berlin, about three-hours'-drive from the coast, in 1948-1949 when trying to pressure the Western Allies into backing off from their plans to introduce a new German currency).
However, because pretty much all people now live on land which is in the current day demarcated by land borders, in the vast majority of cases getting the necessary units into position to blockade a given stretch of land or city basically requires that the opposing sides already be at active war, at which point the blockade is more like The Siege (the only reason the Soviets could pull a ground blockade of West Berlin and not be in an immediate shooting war in the first place was because of the weird legal position the entire city of Berlin was in thanks to the post-World War II occupation agreements the four powers signed) in which case the blockader would want to resolve it as quickly as possible so that those units can move on deeper into enemy territory (or just end the war with a Capital Offensive).
The loose/tight options don't exist for land-based blockades because a loose one would be totally ineffective (you're too far from the target city to do much interdicting of trade because unlike open water there will be trees or buildings or hills or tunnels hindering your own ability to do so); this leaves a tight one as your only choice, which is expensive to maintain and liable for collateral damage. Naval ships with guns, on the other hand, cannot outright invade a city on their own — the most they can do in directly attacking a city is shell it with artillery pieces because you need specialized landing craft filled with soldiers to get into the city itself. Seeing large ships on the seas around your city is a sort of in-between level of threat that by itself non-verbally says, "I am a threat, but I may or may not attack you right now" which allows a chance for diplomacy.
The visual element of ships as opposed to other pieces of military machinery should also be considered. A line of ships on the visible horizon does give those ships a sort of "looming giant threat from far away" quality that's just a touch Lovecraft Lite — an individual naval ship is a lot bigger than even the largest tanks ever used in ground warfare (too big and they'll be too slow or too easily prone to breakdowns); the vast majority of aircraft used today tend towards the sleek and speedy because big-ass airships eventually proved to have big-ass targets to shoot with enough holes to neutralize from the ground.
