why bimolecular dehydration not appropriate for synthesis of ethyl methy ether?

Bimolecular dehydration is a way of preparing diethyl ether from the dehydrating action of concentrated sulfuric acid on ethanol. The dehydrating agent, conc. H₂SO₄ abstracts a hydrogen from one ethanol and a hydroxyl (the -OH group) of the neighbour.By this Sulfuric acid grabs a mole of water.

So this method works only with symmetrical ethers: di[alkyl] ethers. 

Methyl Ethyl ether is better prepared from Sodium ethoxide and methanol or Sodium methoxide and ethanol.

Moreover you will get three ethers if you try to react methanol + ethanol with sulfuric acid at high temp in a bimolecular dehydration reaction. So you will get all possible combinations including ethyl methyl ether, dimethyl ether and diethyl ether.