If random independent life emerges on Earth now it's not surprising old life that had billions of years to optimize for the environment and in general just outcompetes it immediately.

Expecting the opposite would be like betting on a random path in a graph with millions of edges to be faster than a path that was optimized by billions of computers for billions of years.

It's not that old life optimized for killing the new life (it probably didn't because it doesn't seem to be a common enough occurence). It's that the new life would be very likely very bad at everything.