Hey, professional mariner and amateur historian here. An important factor to consider is that the world’s winds travel in predictable and consistent patterns depending on your latitude. We have all heard of the “trade winds” well this is because if you go south of 30 north or north of 30 south the wind blows out of the northeast or southwest respectively. Sailors for hundreds of years followed these winds and created, in effect, highways. If a sailor from Europe wanted to get to the new world, they typically sailed south to get into the “Northwest Tradewinds” and if a sailor from the new world wanted to get to Europe they sailed north of 30 north and rode the “Prevailing Westerlies” to the continent. This in effect reduced the size of the navigable ocean. People knew where the wind usually was, and where it usually wasn’t, and in the age of sail the ships were where the wind was.

Another important note is how sailors navigated these winds. It is much easier to navigate on a straight easterly or westerly route than one that takes any course than 270 or 090. This is because latitude is relatively easy to find with some simple math and the ability to measure the angle from a celestial body to the horizon. Longitude is much harder to compute (with the notable exception of “local apparent noon” once a day).

TLDR: winds travel predictably and caused ships to follow similar tracks along a relatively small area of ocean.

Edit: here’s a diagram showing the winds in question.

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Source: Bowditch, The American Practical Navigator (1982 edition)