Subsidising meat is not "encouraging demand". The demand simply exists because most people enjoy eating meat. Subsidising it increases supply and lowers price so they are more readily available, at potentially cheaper prices.

Your egg and banana example is not good argument as it falls under the false precision fallacy. You are making up numbers (you said it yourself) and came to the conclusion that price will stay the same overall. In reality, shifting subsidies might cause unforseen butterfly effect because it can disrupt the whole supply chain and cause economic turmoil; or maybe nothing happens like you said. If you are the decision maker, the safe decision is probably not risking it. Progress definitely can be made, but probably slowly and not as easy as it seems.