There is your problem. However, even if you're consciously building for low quality, lock washers are still not useful or necessary. You will still have low quality if you remove them.

I think if you want to use a bolt and nut as just a pin that holds some slip tubing together, without unduly compressing the tubing, you want two nuts that are tightened against each other. The tubing likely has a bit of elasticity (likely, all the elasticity you would want from a washer and then some)*, so one nut can be lightly tightened against the tubing, so that the assembly doesn't rattle loose under ordinary movement of the product. There can be washers so you don't scratch the tubing, if that matters. Then you put on the other nut and tighten it hard against the previous nut, while preventing that one from turning any farther. This generates tension in the bolt section between the two nuts, binding them firmly together and preventing them from working loose.

This will cost you more in assembly time/steps and parts; that's what you get from building something that is less likely to fall apart in use.

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* It's entirely likely that the thin wall tubing has a much lower spring constant than a split lock washer. So that is to say, if you tighten the nut to the point that you're deforming the tubing, the washer may still be almost entirely uncompressed. Adding a relatively stiff spring into a "sandwich" that already includes soft springs generally doesn't do anything except past the point where the soft springs are fully compressed.