Two reasons:
1. engineers are disproportionately represented in the early retirement community, so in a way any FIRE resource could be considered "for engineers". ...maybe? Do you buy that? No? Yeah I get it.
2. a couple of weeks back, an early retirement blog that had nothing to do with engineering landed on the front page having also advertised itself as "for engineers." It seemed like an ingenious marketing strategy so I decided to try it out. It didn't work out so well for this app, though. So it goes.