Simplifying the tax code is about tax prep. The simpler the tax code, the simpler to file. Though what you say about him wanting to lower taxes is possibly true, none of those posts are about that.
I might buy that line of thinking for a corporation but the direct file program was about individuals. Elon gleefully tweeted about how that had been deleted. That's a direct give away to TurboTax and H&R Block.
The issue isn't direct file vs TurboTax.
It's whether most individuals should have to file at all.
A few tweaks around employment income and capital gains, and you can do away with filing altogether for most people.