Ah yes, I can definitely see manufacturers opting to be reliant on other manufacturer's charging networks. That's a really great idea.
Lets see your suggestion of how they could have done it better, bearing in mind we are talking almost zero government incentives here, so there is no point going, "well the government should have ..."
The range of initial BEV's was so short, I am pretty sure there was no interest as, who'd want to do a long journey in a car with a 100 miles rage? That was the issue, and Nissan/Renault/Tesla (maybe BMW) were the only ones who would benefit, but not on such small sales volumes, so it all comes down to who was willing to invest, and only 1.5 companies did, and only one has continued to bother. Now there are new players on the scene with Ionity, which only opened their first charging station 3 years ago and are expanding rapidly (pun totally intended), but I already highlighted the issue.
I am glad there are the likes of Instavolt and Gridserve in existence now, BP might eventually pull their finger out and sort out the BP (what ever new name it has this week) network, and Shell could be a serious contender if they wanted to be, but for now it's just a handful here and there. So there will be one network wholly owned and run by a car company, and I can imagine the utter **** show if they open it up and started charging 69pkWh to non-own brand cars, there'd be headlines in every paper ripping them a new one, even if they did just make (almost) everyone who has an EV's life easier. They'd be justified in doing so though, right, or not?