Chairs, like wooden dining room chairs, are some of the most dynamically stressed woodworking projects. A bookcase may carry hundreds of pounds of books but you put the books on the shelf and they mostly just stay there. A dining room chair has people sitting down, scooting forward, shifting around, leaning back, standing up etc. so there's a lot of force moving around trying to bend the frame members and shift the tenons around in their mortises. This often causes the glue, or the wood immediately around it, to fracture under repetitive stress and causes loose joints.

Some woodworkers prefer to use hide glue (or its modern synthetic equivalent) rather than PVA glue specifically because it isn't as strong, and because the bond can be released with heat. That allows the glue to fail while the wood itself remains intact, and then a chair with a failed joint can be disassembled and repaired. A chair assembled with PVA is likely to break in the middle of a board or dowel and is impossible to disassemble in any intentional way.