This is just anecdotal, but in my experience most Christians are not very interested in the Old Testament. And a sizable minority of them are downright embarrassed by it.
You notice this with people who express an interest in learning the original languages of Scripture. Almost always, they default to learning Koine Greek. But the great majority of the Bible is written in Hebrew.
Perhaps this focus explains why so many Christians don’t notice obvious patterns in the way God works. If you spend all your time in the New Testament, and you’re thinking of God’s relationship to people in light of the Great Commission, you tend to become blinkered to the obvious—namely, that the Great Commission is a “late innovation” in God’s approach to saving people.
Before Matthew 28, God’s salvific plan was exclusively through Israel.
Let’s confine ourselves to the postdiluvian world, since that is where we start to get details about God’s covenantal plans. For about half of human history post-Flood, God ignored the vast majority of people living in the world and confined himself to an exclusive saving covenant with a relatively tiny family, which later became a relatively tiny nation.
In fact, not only did he ignore the rest of the world, but he disinherited them. At Babel, God divided the nations and put them under the authority of lesser divine beings (Deuteronomy 32:8-9, ESV), whom he knew would not lead them to salvation but instead rule them ruthlessly and lead them into idolatry (cf Psalm 82:1-3). He chose only Israel as his allotment, and abandoned everyone else for two millennia.
Why would he do this if he wants everyone to be saved?
He didn’t need to divide the nations. He is omnipotent and omniscient; he could have found another way to solve the Babel problem. He could have come down in power, destroyed the tower, kept the people as a single nation and covenanted with all of them. Or he could have divided them but then made covenants with each individual nation separately.
Yet he did not.
And as a result, he condemned everyone outside of Israel—which rounds up to the whole world—to eternal judgment. From Abraham to the cross, with isolated exceptions like Jonah and Daniel that seem calculated to prefigure the gospel, he doesn’t even try to save the world. He doesn’t even try to save Israel most of the time—if you read through the books of Kings, for example, God could have done a great deal more to nip the evil of people like Nebat and Jeroboam in the bud. Yet instead he abandons the northern tribes and remains loyal only to Judah. He effectively limits salvation to a tiny part of a tiny part of the whole world.
This is not to deny that he used Israel to bless other nations.
But it seems gratuitously obvious that God could not have intended to save most people throughout the world for at least half of postdiluvial human history, since he did not try to.
This reflects an obvious pattern that many Christians want to resist: under the Old Covenant, God elected Israel out of the nations. Under the New Covenant, God elects Christians out of the nations. The New Covenant is individualistic rather than corporate. But the same process of election is at work. Israel is a type of the church.
But if Israel is a type of the church, and God chose it as a special people out of the multitude of nations, then why think God has radically changed the way he works? Election may have now become focused on the individual, rather than the nation, but why think God has stopped choosing a special people for himself out of the multitude?
So Arminianism not only cannot explain God’s actions in the past, but runs against the grain of the pattern of salvation those actions establish for the present.