Although Optimus Prime intended to sacrifice himself for mankind. But he wouldn’t be allowed to sacrifice himself just because he wanted to. He was protecting this base after all. He explained the Spark within every Transformer was a mini AllSpark without its unique power. The Sparks radiated a power that protected nearby mechanical objects from the AllSpark’s power.

“The Spark’s powers are separated into two attributes much like Yin(dark) and Yang(light). If the Autobots’s Sparks are Yang, the Decepticons’ Sparks are Yin. Hence as the two parties of Transformers nears each other, they could sense the existence of the other even in their vehicle or object forms. Which means our plan to sneak into the Decepticons’ city becomes impossible as soon as our weapons become affected...