Consolidation, not commoditization. Cars aren't barrels of oil or truck cars of coal.
It's just impossible to compete as a car company unless you are very niche, a billionaire or a state. The big 3 vertically integrated to the hilt and erected monumental barriers to entry and then became very, very conservative.
https://www.whichcar.com.au/car-advice/car-manufacturer-bran...
We have numerous Korean, Japanese, German, and American vehicles on the road with many varieties of sizes and performance.
And obviously you will need to have deep pockets to enter the car business, why wouldn’t you for such a complex machine? That does not mean there is excessive consolidation in the market.
"The big 3" is a phrase referring to the US automakers; Ford, GM, and Stellantis (formerly Fiat-Chrysler).
On a global scale you also have giants like Toyota, Volkswagen Group, Hyundai Group, Renault–Nissan Alliance, and Geely.
These companies make most of the brands you've heard of.
Obviously the barrier to entry to manufacture a hugely complicated machine will be high, but the data indicates it is not impossibly high.
When Toyota sells 10 million cars a year it's not news, they have basically reached peak growth. Tesla's valuation is higher because they keep selling more cars and still have room for growth (and because of Elon Musk himself).
The only differentiation that can arise then in is in terms of branding. That's exactly what cars are now. Identical metal boxes, captured by marketing, purely differentiated on intangibles like brand identity.
And even this differentiation is becoming less and less relevant. How many people still really care about their cars? (mostly men do, and even that's waning). They're basically washing machines now.