Wood itself is sustainable, but in making a choice of building materials, we're also looking for total embedded energy cost and impact of the final product. Traditional buildings from a century ago relied on the harvest of old-growth wood with denser rings than the new sustainable forestry, and they were built with fewer features - when built well they didn't fail, but they weren't targeting high energy performance, climate control, dust and mold resistance, etc. We can't go back - we could lower our standards but the stock of old-growth remains depleted. New wood constructions often use processed and glued timbers because the processed timbers can be lighter(good glue is really strong) and they don't experience nearly as many quality control issues(solid wood tends to warp).
The thing is, once we start looking at wood in detail, it's never just wood. It's wood, plus adhesives, paints, and finish. You can't use just wood because it rots - you at least need to add some pigment to block UV rays and drainage to limit water pooling. Each of those additives are a potential source of VOCs(volatile organic compounds, the term that more accurately describes "chemicals"). And each step taken during processing adds energy cost. Paper and corrugated cardboard are not innocuous - they use one of the higher-energy processes relative to the amount of input material.
When you look at what you can do besides wood, you get similar tradeoffs. Stone is great, but it's still hard to work with directly, hard enough to not scale to our industrial population - as it stands, you need an artisianal economy of stonemasons to make those huge ancient constructions. Concrete has a huge climate footprint and the dust is a major VOC source. Steel is high-energy and not abundant enough to be used everywhere.
Thus, plastics enter as a way of getting some of the qualities we want. Plastics are not all one of a kind and have varying VOC content. We can't afford not to use them to have this population and quality of life, which means we have to study how to use them safely. The microplastic issue is a part of that, but it's oversold as "plastic is scary". Wood smoke is also scary, as anyone who has been around a wildfire will attest.