I'm guessing you don't live in the US, or your friends are underpaid, or they work for a firm that chooses, but does not have to, provide overtime. Actual engineering should generally be considered exempt from overtime.

1. If nothing else, engineers are considered a learned professional.

2. They probably make over $100,000 per year.

3. They may hit the executive exemption.

https://www.dol.gov/whd/overtime/fs17a_overview.pdf