2) Why do they not unlock this range all the time?
I see people covered the technical details of which batteries have the controlled locking, but not a lot of discussion of why.
It is a sales thing called "lowering the barrier to entry". Makers of computer chips, like processors and memory have been doing this kind of thing for a very long time and still do. Let's say they (Intel or AMD or somebody) are building the processors that are capable of 3 GHz speed (or maybe multi-core processors with X number of cores), and they have some price--say $200. So there are some people who would pay that $200 price, but for others, they feel that's too expensive and won't buy. That could be limiting their market if they can't sell as much.
Well, they might want to offer a cheaper product to attract some of those buyers, right? But it costs a lot of company overhead to design a new less capable chip. And they would have to keep two separate product lines going in their factories. And they would have to track and manage those separate product lines and inventory and shipping and storage and etc. etc. etc. So what they sometimes do is just create a fake "new" product which is just a slightly locked version of what they are already making--maybe a slower clock speed or not using a couple of the cores--and they sell this at a lower price. That is cheaper than designing an additional part and probably still is somewhat profitable and can attract in some additional customers because of the lower price.
(Side note: I do work in the computer chip industry, and some of this is not just for sale/pricing reasons. Some amount of the parts in testing can't quite meet the top speed ratings, so they are marked down to be sold as slower speed types of parts because that's the functionality they can meet. But depending on where the demand in the market is, they may also mark some of them down to that slower speed on purpose just to have more of those types to sell.)
The companies may or may not even announce that the "different" cheaper product is a locked thing. Tesla does say that, but other companies sometimes may hide that.
So similar procedure with the Tesla batteries. They had gone to the 75 battery size, and for a period of time, they wanted to goose sales a little bit and thought people might be shy of the full price, so they created the locked 60 and 70 battery versions to be able to offer cars for sale several thousand dollars cheaper to attract some more buyers. And offering the option to unlock that extra capacity kind of left the tempting opportunity where they might get some of that extra money back later if people chose to buy that unlock.
However, this is not something they are going to do most of the time or for most of their very high volume products. They only do it to create some small-selling version of something that they don't want to support in high numbers. The battery cells are one of the most valuable parts of the car, and the thing they are constrained on the most in their supply chain. They won't want to give those away without being paid for them. And giving away a lot of cells like that would reduce the number of battery packs they can build, which equals the number of cars they can sell. So they don't do that locking thing often.
