Earlier quoted context omitted.
Lumber isn't a permanent removal from the carbon cycle. Wooden structures have a shelf life, and eventually the wood decomposes and re-enters the carbon cycle. The only way to sequester carbon via lumber would be to bury it in a way that prevents decomposition. I don't think this is an especially efficient method of carbon capture.
By the same measure, CO2 is not a permanent state either, but it's an issue because of the imbalance in dynamic processes - The carbon stored by lumber is the amount of lumber in the world minus decaying lumber.
In 2014, use of wood products in all notable categories combined was about 1.25 billion tons [3]. Including just sawnwood and wood paneling, it was 0.827 billion tons. Since there's no plausible way to use 2500% as much lumber for structural purposes as we do now, and just harvesting wood and leaving it outdoors will lead to decomposition on short (decades) time scales, people consider charring it and/or burying it underground. Just building more structures out of wood is barely going to put a dent in the problem.
Likewise, dynamically shifting the equilibrium toward wood from CO2 doesn't help much if the wood persists for only decades. The time scale for CO2 to naturally return to its pre-industrial equilibrium is more like 100,000 years [4]. We need sequestration measures that prevent CO2 from returning to the atmosphere over longer time periods than wood takes to decay naturally.
[1] https://www.statista.com/statistics/276629/global-co2-emissi...
[2] https://en.wikipedia.org/wiki/Cellulose
[3] https://www.forest2market.com/blog/fao-report-highlights-res...
[4] https://www.amazon.com/Long-Thaw-Changing-Climate-Princeton/...