Learn Spanish (Latin America): No la compro porque es una imitación. - I am not buying it because it is an imitation.

In colloquial Latin American Spanish, you can repeat a noun to emphasize that it is the ultimate, truest, or most stereotypical example of that thing. If you said es una imitación imitación, you would be emphasizing that it is an absolute, undeniable knock-off, and not just something vaguely similar to the original.

Why is it la compro and not lo compro if the English translation just says 'it'?

In English, 'it' doesn't have a gender, but Spanish pronouns must match the noun they replace. Here, la replaces a feminine noun that was mentioned earlier in the conversation (for example, la bolsa or la camisa). If the speakers were talking about a masculine object like a watch (el reloj), the sentence would use lo instead: No lo compro.

Why is es in the indicative mood? Doesn't expressing a personal reason sometimes require the subjunctive?

Porque (because) states a fact or a reality, so it almost always takes the indicative mood, as seen here with es. You generally only use the subjunctive after porque in negative clauses where you are specifically denying a reason (for example, No la compro porque sea falsa, sino porque no tengo dinero — 'I am not buying it because it is fake, but because I have no money'). Since the imitation is the actual, affirmed reason here, the indicative is required.

The translation says 'I am not buying it', so why does the Spanish use the simple present () instead of the continuous ()?