Marathon racing (has become) increasingly popular among amateur athletes in the last few years.
Why is this sentence correct? Isn’t “last few years” past, not present perfect?
Making that change would slightly change the meaning of the sentence. As it’s written, the trend is that marathon racing is STILL increasing in popularity. If we changed it to simple past tense, the sentence would be saying that the popularity of marathon racing recently increased for a few years, then leveled off. Maybe? I feel like explaining the subtle differences between tenses is not my strong suit.