This question is more than a bit ironic; without the millions and billions of chemical reactions that we each are composed of, it couldn't be asked. Two books come to mind here: The Watchmen (specifically Dr. Manhattan) and Godel, Escher Bach by Hofstadter, which you may (or may not) enjoy reading. Also this:https://en.wikipedia.org/wiki/The_Siphonaptera. There are only two thermodynamically stable minerals: quartz and darn it, I've forgotten the other one! So when you look around you, virtually nothing you see is chemically or physically stable. (Arguably, water is stable too but it is slowly being lost to space, although you and I won't have to worry about that.) So we need to be aware that most of what is going on around us we are unaware of. (Thank goodness, most of the creepy crawlies living on and in us are the stuff of nightmares..)
Anyway, while you are unaware of the sea of microbes that we are surrounded by, and of the countless chemical reactions going on around us (did you know that concrete generally has a lifetime of only 20-50 years?) that shouldn't imply that our environment is chemically inert.E-pusher mentioned activation energy, chemists generally think of it as the hill between two valleys, where the two valleys are "stable" chemical compounds and the hill is the "activated species".
For instance carbohydrate (like wood is mainly composed of) is one valley, and $\ce{CO2}$ is the other (lower energy) valley. Wood doesn't seem to do much until you light a match to it (providing enough energy to push some of it up the hill). A lot of our natural world is composed of polymers. Unlike small molecules like water or sugar, polymers (like carbohydrate, protein, plastic, paint, DNA, RNA, etc.) are typically very slow to react. It's also very difficult to get them to diffuse or dissolve (many of them, anyway).
At the other extreme, take a piece of aluminum - say an aluminum nail or screw. Cut it (or just scratch it). Within microseconds, the surface of the $\ce{Al}$ is oxidized to form a film of $\ce{Al2O3}$. Most of us don't ever realize that aluminum is a very reactive metal, much more reactive than iron or steel. One reason that we don't see many reactions occurring, is because if they did, then the object they were occurring on/in wouldn't be very useful. (Of course, cooking is just a series of (useful) chemical reactions, which allowed us to reduce the energy we needed to digest food and was probably one reason we developed intelligence).
Anyway, the basic reason why we can surround ourselves with all sorts of materials which don't seem to degrade, is due to the need for the reaction to get up that activation energy hill. Even a reaction as simple as $\ce{2H2 + O2 -> 2H2O}$ doesn't proceed very fast at room temperature (unless a catalyst, such as $\ce{Pt^0}$ (with a clean surface) is present and then whoosh!).
By the way, all of my kids are long grown up and gone, but I've still got some of their polyethylene toys around. The plastic looks almost like new, but squeeze it, or drop it, and it cracks and breaks, even though when it was new, the toy was very tough. Even polyethylene ages, and undergoes oxidation reactions. Makes you wonder about all of the plastic plumbing pipes in homes, huh?