Learn Turkish: Bazıları sentetik ilaç yerine organik meyve tercih eder. - Some of them prefer organic fruit instead of synthetic medicine.

When you say "instead of [a general thing]", the noun before yerine doesn't take a genitive (possessive) ending like -ın or -in. You would only use the genitive if you were talking about a specific thing, like bu ilacın yerine (instead of this medicine). Since "synthetic medicine" is a general category here, it stays bare: sentetik ilaç yerine.

How exactly does bazıları break down to mean "some of them"?

It is made of bazı (some) + -lar (plural) + -ı (third-person possessive suffix). The possessive suffix gives it the "of them" meaning. When you want to say "some of the people" or "some of them" as a standalone subject, bazıları is the standard pronoun to use.

Why use the aorist tense (tercih eder) here instead of the present continuous (tercih ediyor)?

The aorist tense (the -er ending here) is used for general truths, routines, and personal habits or preferences. Because this sentence describes a general fact about what some people prefer in life, rather than an action happening right at this moment, the aorist is the most natural choice.

Why are ilaç and meyve singular when we are talking about them in a plural or general sense?