It cause everybody wants them all of the sudden and the manufactures can not keep up to the demand.
Shooting Economics 101.
When America has a republican government they are softer on guns but fight more wars and need more ammo.
Consumer prices go up
When America has a democratic government they want to fight less wars and are tougher on gun owners.
Consumer prices go up.
Either way components are getting harder to get a hold of. Especially north of the USA border.