That is because there are no weights to begin with. In actual biological neurons synapses perform a rather complicated biochemical dance involving vesicles, ion

That is because there are no weights to begin with. In actual biological neurons synapses perform a rather complicated biochemical dance involving vesicles, ion channels, second messengers, whenever an action potential arrives. Some of that can be described by simple ODEs which might contain a constant that you could call “weight” but the actual physical synapses know nothing about that.