look up subsidies to milk-producers

the price is still high compared to milk because milk is selling for far less than it should be (even if you completely ignored environmental cost) and many oat milks try to match that price-point as good as they can and are even selling at a loss (see Oatly)

a lot of food is costing very little in comparison because the government is subsidizing it - shifting subsidies away from meat/dairy would make them cost more and potentially bankrupt local farmers - I just don't see that every happening with how many people are thinking they have a right to eat meat every day

also for example in Germany there are two tax-brackets for sales-tax the standard 19% or the reduced 7% - "basic-foods" are taxed at 7% and that includes milk and meat while oat-milk and meat-replacements are taxed as "special food" at 19% so that's also a barrier that you just can't break down by scaling better

there are a lot of levers but pretty much all of them will have to result in meat and milk prices rising deliverately because of politicians - don't tell me that you believe that this won't result in a fundamental shitstorm against them...

Oat milk is that expensive because hipsters don't care and pay that price. They aren't only selling a sustainable milk alternative, they are selling a lifestyle. There is not much of a conspiracy aside from companies charging the maximum that customers are willing to buy.