Why Are Alternative Milks More Expensive Than Dairy?

That's not the case in Holland; with soy milk costing 0.89 [1] and cow milk costing 0.99 [2].

[1] https://www.ah.nl/producten/product/wi565765/ah-terra-planta...

[2] https://www.ah.nl/producten/product/wi450534/ah-houdbare-hal...