Because everyone has $400-500 to spend on a first-time entry-level road bike on top of the cost of accessories, locks, tools, and likely a new saddle which easily jumps the cost up to $600 or more.
To be honest, you sound like snob. Use cases exist where $600 for a bike setup doesn't make sense.
Maybe I'll do an overhaul of all the components on the bike once I'm really into using the bike and want more out of it, but for now there's nothing wrong with it after replacing the pedals, saddle, brake levers, and chain.
As for your comment on not doing research, I've been doing plenty of it. However, I'm still very new to learning about bikes and don't know everything. Something was on sale and I wanted an immediate answer because Amazon prices fluctuate frequently and I didn't want to miss the sale.