It all comes to risk vs reward and the law of diminishing returns.
500mg is just a sweet spot to get you into the 2000+ Test level range.
Some people need more, others less.
Also everyone's body metabolizes compounds differently. You may get to over 2,000 total test with less than 500mg or you may need more (assuming all else is equal like quality/brand).
Again its just a guideline and a lot of people have run that level with fantastic gains while minimizing side effects. Testosterone levels that are too high for too long open you up to heart issues, estrogen issues, prostate issues, etc.
In the end you need to decide whats the best level for you and what you are trying to accomplish. To be honest I like test at 300-350mg/week as opposed to 500mg/week. I liked the look/feel at that level. My AI was dialed in and everything was spot on but just felt and looked better at the lower level. Personally i will never run test at 500mg/week again. Id rather use a 200mg/week dose coupled with Deca, Primo, EQ, etc.
Just my opinion though.