not getting all it's proper maintenance

So when my wife and I started dating, she had been given a car by a sister. That car had 150k miles on it and it got oil changes every 20k miles. In the 90s. Pre-synthetic oil.

Her family (aside from her oldest sister, who has been telling them all the same shit for decades) wonders why my/our cars have always been so nice, and I keep telling them "just keep it clean and do the recommended maintenance". I don't know if they think I'm keeping a secret or lying to them, but it's that easy.

As I've primarily rented (nothing much beyond standard rental contracts except a couple double nets, but I knew the owners and they preferred me to their usual maintenance guy) I'm suddenly wondering if I have been forgetting to rotate my foundation or something.