The lipid is both hydrophobic (tail) and hydrophilic (headgroup). Its mechanism of action is to form micelles to transport the mRNA (ie nanoparticles). These micelles/formulations are engineered specifically for a route of entry. You can quite easily destabilize micelles with a change of pH such as the GI tract.

Ingesting something is (usually) completely different than injecting, especially when these 'vaccines' dont work in the first place.