Well if you think about it, lacto, pedio and brett exist naturally in the environment on stuff, in the air, etc. When your equipment sits in storage it gets all that stuff on it. That's why we sanitize before post-boil wort or beer touches anything.
The difference with sour beers is that you're creating big pools of those critters and they soak in the equipment which increases the likelihood that they can get into a scratch, small cracks, etc. and not come out with a spray from a spray bottle. Anything I have that touches a sour (or infected) beer gets a long soak in starsan for a few days. I fill up the fermenter and bottling bucket with starsan and then dump in all the tubing and let it sit for a few days. Then I dump it out and put it in storage. I haven't had cross contamination yet.