The particleboard connections aren't very sturdy.
Also the assembly for ikea stuff is usually perfect.. everything aligns to the last millimeter... which again, I can't say for much more expensive furniture pieces.
It's a few extra dollars and will make the pieces survive a move and just generally feel sturdier. It's not a replacement for "good" furniture but will make the cheap stuff much better.
And most people can't differentiate between quality (nor should we expect them to!).
"Proper" furniture stores you find in malls and outlets are generally high margin crap. There's lots of soft scams out there.
There's a reason many people go back towards antiques and similar.
Probably because the ikea stuff you bought tend to be particleboard and the "expensive furniture pieces" are solid wood. Solid wood tend to wrap/deform more due to moisture than particleboard, which means even if they're drilled with millimeter precision at the factory they end up not aligning when it reaches your house. From personal experience the solid wood furniture I got ikea were definitely not aligned "to the last millimeter".
What? How?
I’ve moved a lot in the last 15 years and always defaulting to ikea for convenience. “Fits together well” isn’t what I’d use to describe their furniture.