I have a theory regarding plantar fasciitus, which may be all wet, but I've fought it off and on for years and years. I work twelve hour shifts on concrete, and am thick, so boot issues show up fast! I also do a LOT of walking and hiking.
I think it comes down to foot support. Years ago, when boots were less disposable and not all made in the Far East, I only had plantar issues after wearing my boots to death. As soon as I got a new pair, the issue fixed itself, with some stretching and babying for a bit, then I was good to go again.
Fast forward to the last twenty years, when the majority of work boots are basically glued together crap, produced at the lowest unit cost. Even once decent brands like Redwing die faster, and foot pain comes a LOT quicker. I've had to invest in new boots more often, and the better the boot quality, the longer the interval before the foot support goes away. Once it does, the plantar issues creep up again.
My personal feeling is that the poorly made boots use poorly designed and composed footbed materials, that compress too quickly, and move way to much. Once your foot loses that support, its only a matter of time before issues crop up.
My advice is to buy the best boots you can afford, and find a last that really fits your foot. This varies tremendously from person to person. Good boots cost lots of money :/ A couple of my favourites are Danner, and Zamberlan.
A cheat you can use with a cheaper boot, is to find orthotics, or use an insole like Superfeet (Nylon, feel like boards until they break in, but support REALLY well), or some other way to add that all-important support that keeps the pressure spread out on your foot, and keeps your foot from flexing too much with each step.
Good quality boots, and high quality footbeds are what has kept my feet from pain, for a long time now.