That's not strictly true. Depending on the company, it's very possible for mere engineers to have access to material non-public information. There's a reason many companies impose broad blackout dates on trading.

Mere engineers would be prosecuted long before CEOs for the totally-at-Justice-Dept-discretion crime of "insider trading".

That's self-evidently false. Engineers have insight into the internal culture of a firm and how it may differ from public perceptions, not to mention their own opinions on the quality of the back end technology and awareness of future plans or possibilities.