Why is “compro” used instead of “que he comprado”?

Hola Jessica H.

Great question!

In Spanish, when talking about the number of times something has happened up to now in the current time period (like this year, this month, today…), it's very common and perfectly correct to use the present tense rather than the present perfect, especially in Spain.

→ Literally: “This is the third car I buy this year.”
→ Idiomatically: “This is the third car I’ve bought this year.”

The English present perfect (have bought) matches the Spanish present (compro) here due to this difference in usage between the two languages.

But you’re right that grammatically, you could say:

It’s just that native speakers often prefer the simpler present in this kind of sentence.

Hope that helps clarify the choice!

Hasta pronto

Silvia