You might be interested in this YouTube video which discusses the issues of 'big seed' in regards to tomatoes. I'd imagine the same applies to any commercially grown crops (another comment mentioned that there is basically only one commercial variety of bananas), which would explain why jalapenos are less spicy than they used to be.
https://youtu.be/ngjAqzam0fU
TL;DW;
- Almost all commercially grown crops are from hybrids, which means two varieties bred to produce a new variety with the selected characteristics of both.
- The characteristics that are chosen are those which are most commercially viable: long shelf life, visually appealing, size uniformity - these are often at the detrement of other characteristics such as flavor, nutrients or in this case heat
- Hybrid plants usually do not 'remain true', meaning their offspring will not have the same characteristics. This means farmers need to buy new seed each year to maintain the same characteristics. This results in hybrid seeds being very valuable - some are worth 10x more per kg than gold.
- Hybrids seeds are produced by pollinating plants by hand. This is a time consuming process, and usually done in low income countries. That means labour laws are often ignored, and child labour is a big problem.