Jalapenos are not really hot peppers. The hotest are probably Jalapeno M, Rome, Mucho Nacho and Billy Biker. There are even no heat jalapenos. It could be that your taste buds have grown acustumed to hotter types. Rome goes a shade over7000 scu Jalapeno M pushes 5000 scu.

Agree that while there are many varieties of jalapenos all with varying degrees of "heat", it is basically our individual taste buds that determine how 'hot' they are. Taste buds age and they adapt based on exposure over time. Store varieties are unknown but which variety have you been growing? Also be sure to cut back on watering to improve flavor. I prefer Guatemalan Jalapeno (seeds from Pepper Joe's) and Rome is too hot for me personally. Check with the folks on the Hot Peppers forum here for more suggestions.
Dave

I had the same problem with local jalapenos, I got a biker billy and that gives a nice heat.

Last year I grew Jalafuego from Johnny's and it was nice and hot, and plenty productive. Still eating salt-fermented ones, and dried lots more from only four plants.