Why is evolution considered theological?
Because it leads to the questions: who made the natural laws that cause evolution? Laws are legislated - were they legislated by an overmind, or did they come into being without intelligence, themselves the product of random accident?
It all goes back to the question of the uncaused first cause. Natural law MEANS cause-and-effect, going backward in a chain. Eventually, you get to the first domino. Who or what made the domino, and what made it fall, and why is it that there is a law that it falls, and why does its fall cause the next thing to happen. Who or what set the parameters of cause and effect?
Naturalistic evolution views the living creature as a meat machine, a sophisticated interaction of chemicals, behaving as they must under the natural law. Evolution, then, is the inevitable result of the interaction and permutation of these different chemicals over oceans of time.
The theological question remains in a very ancient universe where everything evolved chemically and physically from the Big Bang - why is there natural law, and what caused the Big Bang, and what caused whatever there was that existed as the material OF the Big Bang.
The theologist says "God is the uncaused first cause."
The atheist rejects that answer as a cop-out, and seeks to extend back the cause before the Big Bang - in string theory, for example.
The ultimate atheistic solution is to find a "diesel-engine universe" that, through strings, expands and contracts in cycles-of-cycles forever, in both directions. If that is so, then there is no "first", because the "first cause" of THIS manifestation of the universe is merely the FINAL act of the last universe, returning to a Big Crunch. Then one can have a material nature that "always was and always will be".
Alas, there does not appear to be nearly enough gravitational sources in the universe to pull the expansion back together, so our universe looks to be a unidirectional arrow, a ray from a starting point, rather than the dot on a number line that stretches forward and backward forever.
These matters are ultimately theological at their core.