It's not just your imagination, jalapeños in American grocery stores have indeed become less spicy.
A recent episode of the podcast The Sporkful explored this phenomenon, consulting experts to understand why jalapeños have lost their heat.
After one scientist developed a mild jalapeño to appeal to consumer tastes, this variety became a dominant crop.
This shift towards milder jalapeños has led to a noticeable decrease in their potency, confirming observations made by many, including the author's mom, who has switched to spicier options like serranos and habaneros.
Author's summary: Jalapeños have become less spicy over time due to a shift in consumer preferences.