God has by now certainly proven himself to be quite strict, as in, just for example, ordaining capital punishment for murder (Gen 9:5-6). How and why, in his original examples of law enforcement, is God initially very strict?

Let us review his strictness. Consider the examples. For their original sin of eating a piece of forbidden fruit, God exiles Adam and Eve from the Garden (but not entirely from the presence of God), and assigns them limited lives of toil and pain. He punishes Cain’s murder with exile from the presence of God and God’s people. He destroys mankind for their unmitigated wickedness, except for Noah, who walked with God, and his family. Though it was Noah who issued the curse on Canaan, it seems God did carry out the sentence (as the Bible’s history books, especially Joshua, make very clear). And when man outrageously attempted to build a tower to heaven, God confused human languages and scattered the people. Later, when the Pharaoh refuses to obey God and honor God’s people, God devastates the land. And when two of the first priests fail to strictly follow God’s rituals, he destroys them. All of these examples, without exception, show God’s first punishments to be surprisingly strict, indeed, harsh. And yet, also in every case, many later examples of the same (and worse) crimes are not touched by God. I believe God literally made an example of the first in each case: the first sin, the first murder, the first corrupt society, the first disrespect of parents (or perhaps the first incest), the first organized occult attempt to displace God, the first oppression of his chosen people, and the first disrespect of priestly duties. God demonstrates in this way both his high standards and his sovereignty. Afterward, it is mostly whole nations (and their leaders) that God personally punishes, and often the punishment still takes place at the hands of other nations.