The problem is brands being tied to ICE, and the value of brand.
I think you are correct that big brands have a vested interest in ICE cars and doing anything off that line risks confusing their message, however I think your proposed solution might actually accelerate the inevitable. There seems to be a misguided assumption with many auto journalists and others that there is only room for 5 or 6 big car brands worldwide. That was fine for our grandparents, but our children care much less about brand loyalty and much more about "cool" factor. Our current generation (you and I) will suffer through the churn of transition, but our children will wonder why this discussion even took place. They aren't interested in mass market products at all, but seek to surround themselves with things that make them an individual.
Look at the music industry up to the late 90's, which was dominated by a handful of record labels. Now the notion of a record label is falling by the wayside - my son is a music producer with a professional studio in his house that is for hire by anyone who wants to record a song. That would have been nearly impossible 20 years ago, but that industry is now on the trailing edge of change and it happened in spite of the traditional stakeholders trying to maintain control.
As ShadowRealm points out the car industry is next, but moves a lot slower. But look at the number of boutique auto manufacturers that have grown out of garages in the past 15 years - including Tesla. None of them are trying to be the next Toyota because that's not what the next generation is going care about.
It's going to take a while and Tesla may not be a company that survives, but they have lain the groundwork to fragment the old established auto industry - the last of the industrial-age dinosaurs. What Tesla has done, that big auto is fearing most, is to show every future auto entrepreneur that once electric powertains are a commodity, the rest of a car is just a bunch of bent metal and cheap electronics. Like the recording industry, the auto industry will come to terms with no longer maintaining a stranglehold on buyers just because they build an ICE with a unique power curve or fuel economy.
In the end it isn't that any of the big brands don't have the money and know-how to produce a Tesla-like car, but they'll have trouble to sell it because the emerging generation won't be interested in conformity. I could have bought a Prius or a Volt but didn't in a large part because I didn't want a Toyota or Chevy. It had nothing to do with capability or features. I bought a Tesla specifically because it helps make me unique.