There's quite a few threads / projects where people have used toolpacks (intact) as ebike (and other) power sources, but it'll take some poking around to find them, as they don't all use a consistent terminology to make searching easy. But they'll give you some idea of how people have already done this.
Regarding the comparison to AA, AAA, C, D, etc: most of the ebike (and toolpacks, for that matter) use the same format: 18650. So you can swap out cells when they go bad, as long as you have the tools to do it.
The catch is that there's a number of different chemistries used in the same physical format, some of which are different voltages, and many of which have different capacities and charge/discharge characteristics, so you do have to check the cells you're replacing and get similar ones to put in it.
As for manufacturers making consistent stuff (pack shapes, sizes, connections, etc; controller types/shapes/sizes/communications/etc)--they have not only little reason to do so, they have every reason *not* to do so, because they'll sell more stuff if nothing is compatible with anything else, as it'll make you buy whole new systems whenever the old one has any kind of problem.
It's wasteful and stupid in the long run, but in the short run (which is all any company cares about), it's highly profitable. :/
Unfortunately what end-users want, and what manufacturers find profitable, are not that often the same thing.
Since people will still keep buying new things rather than fixing old ones, manufacturers have no reason to change their ways. To make them change it, you'd have to get almost everyone to stop buying anything new that was not completely compatible with all the old stuff. Since that won't happen, we're stuck with the system as it is.
As for "oil companies" doing anything, I don't know what that has to do with ebikes/ev's; those oil companies would be as (or more) likely to do even worse than the existing manufacturers. Look at ICE car manufacturers and the "model year" crap they do, where whenever they can they'll change things just to change them so that people have a reason to ditch their old perfectly-working vehicle for a new "snazzier" one.
Regarding costs of ebikes....the prebuilt ones companies make generally are expensive, and are going to be proprietary simply because it makes those companies more money to do it that way.
It can be a LOT cheaper to roll your own, down to only a few hundred $$; less if you already have battery systems you can use to power it (though as noted previously this is not always as simple as one might think at first glance, as your existing packs might not have sufficient current delivery capability, or capacity for range, etc., unless you parallel sets of them). The biggest cost is usually the battery, so using existing stuff (if you have any) saves some money. The motor, controller, and accessories can cost less than $200 if you look around hard enough, and don't expect any support from the seller (and don't care who actually makes the stuff, cuz you'll likely never really know). Then install them on an existing bike that fits you and your intended usage.