why does everyone have spider mites?

i really dont understand how almost every local indoor grower i know excluding greenhouses, has spider mites. seems like everyone outdoors or with a green house has them. i had them 2 different times in my life. once i took in an outdoor plant. another time i took a plant from a friend that was infested. ever since i thought enough is enough i cant trust peoples plants anymore i really hate these spider mites. i figured you wanna do it right you gotta do it yourself. i have a medium sized garden and grow about 20-30 plants. legally caregive for 3 medical patients. all different stages of growth so i have a perpetual harvest. that last plant that had mites i got rid of it. used dr doom bombs in all the rooms. then cleaned everything with bleach. treated every plant with mighty wash. never since have i took anything in. only clones from my own mother plants or start from seed. it's been over a year now and i have yet to find a single mite. i dont even do a preventative maintenance for them. i just cant find them anywhere. all my friends are just too retarded and take in plants from anyone. none of these strains are anything super special. all these top strains are available on attitude, nirvana, single seeds, or several others. fungus gnats i always see here and there. i've actually even seen them fly in through the window around my aero cloner. i rarely find them though cause i alternate and treat with azamax, dr doom, spinosad, and pyrethrins concentrate mixed with water. keep temps high and dont let your night temps get too low and you shouldnt get mold as long as you keep clean. humidity low also but some species of powdery mildew doesnt need much humidity to survive. azamax is a great treatment for it. if you see really white stuff on your buds that dusts off easy, it's not crystal, its mildew! one of my friends thats been growing for years refused to believe me after telling him that about his plants the other day. he swears is crystal but i know it is pm.

this is old news to many but thought some may learn from my previous mistakes.