Are the trucker unions very strong?
What do you need to appease the unions for if there are no truckers?
Can slow the speed at which regulation changes, existing companies react, etc. You mentioned supply limitations. There's also charging infrastructure limitations.
And the up front investment may be too costly for many companies
We’ll see if TuSimple or Tesla succeed in a commercial AV truck by 2025. If so, 2040-45 is my estimate (depending on the factors above)