You're right of course. But many of us, once we know we have PCa, even an indolent one, worry about it and opt to have it treated. You are worrying about it and you don't even have it!
If someone has a Gleason 6 or 7, there is a case for "active surveillance". But there seems know way of knowing when, if ever, a supposedly indolent PCa will turn nasty. So it's a crap shoot, with your life at stake. As you say, it is an individual choice as to whether you want to run the risk.
In my case I was Gleason 8 at age 63. Now if I had a biopsy at age 40, it seems likely in retrospect that I might have been a Gleason 6. By delaying treatment for 23 years (via a long period of "unwatchful waiting"!), I have had 23 extra years without ED. So I don't regret the delay, even though I know that there is a chance that it may have shortened my life. I have traded quality of life for some of the potential quantity.
Age 63. Other than cancer, in good health; BMI 20
Pre-op: No symptoms; PSA 5.7; Gleason 4+5=9; cancer in 4 of 12 cores
7 March 2008, RRP, non nerve sparing
Two nights in hospital; catheter and staples out after 7 days
Continent, no pads needed from the get-go
Post Op: Stage pT2 M- N-; clear margins and lymph nodes; Gleason 4+4=8; prostate weight: 37gm
6-week and 7-month PSAs: 0
Bimix injections working well