It's not that He couldn't, but rather that macro evolution isn't the way that He chose to work. It is to His glory that He created all things fantastically complex and complete. He didn't need millions and millions of years. All He had to do is speak. He did create life with the ability to adapt and have variation within a kind, though.
Genesis 1:11 And God said, Let the earth bring forth grass, the herb yielding seed, [and] the fruit tree yielding fruit after his kind, whose seed [is] in itself, upon the earth: and it was so.
Gen 1:12 And the earth brought forth grass, [and] herb yielding seed after his kind, and the tree yielding fruit, whose seed [was] in itself, after his kind: and God saw that [it was] good.
Gen 1:21 And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that [it was] good.
Gen 1:24 And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earth after his kind: and it was so.
Gen 1:25 And God made the beast of the earth after his kind, and cattle after their kind, and every thing that creepeth upon the earth after his kind: and God saw that [it was] good.
Gen 6:20 Of fowls after their kind, and of cattle after their kind, of every creeping thing of the earth after his kind, two of every [sort] shall come unto thee, to keep [them] alive.
Gen 7:14 They, and every beast after his kind, and all the cattle after their kind, and every creeping thing that creepeth upon the earth after his kind, and every fowl after his kind, every bird of every sort.
Gen 7:15 And they went in unto Noah into the ark, two and two of all flesh, wherein [is] the breath of life.
Gen 7:16 And they that went in, went in male and female of all flesh, as God had commanded him: and the LORD shut him in.
The evidendce of His Creation says othewise. The available physical evidence doesn't support the literal account of Genesis, and geological and radiometric evidence contrdicts the Ussher chronology.
The theories that try to explain the physical evidence in the fossil, radiometric, and geological records as a result of Noachian flood are hoplessy contradictory. They posit ocean conditions required to attain the fossilizations that would have been lethal to all aquatic life on the planet. They describe pheonoma like "hydrologic sorting" that should be easily reproducible in a lab, but can't be. They rail about evolution "violating the laws of thermodynamics" and then theorize about accelerated radiometric decay at rates that would have vaporized the planets crust without any thought to explaining where all that heat went. Asking them to explain it is taken as an invitation to correct the problems with your personal theology and teach you how to "get right with God".