Honestly I don't see that the battery pack for Tesla cars is in the same ballpark as mobile phones or even regular car batteries. The battery pack for a Tesla is a huge lot of cells and no one man can lug that around or replace it.
I'm assuming you're not familiar with this chap?
Who often does just that. Sometimes using only a bread knife! And along the way, provides interesting and amusing insights into the wacky world of Tesla.
The fact that you can only have it replaced by Tesla is, at the moment, logical.
Tesla doesn't do logic. Initially it was supposed to be a lot more open, and encourage the maker community to do cool new things with 'their' cars. Now, if you want to have anything other than Tesla-approved fart sounds, you'll need to be a proper hacker or wait for Tesla to release that feature.
Along the way, that's lead to other shenanigans. So originally in order to get the most value from Federal EV subsidies, you were meant to be able to do a battery swap instead of wait for your pack to recharge.. A requirement that was never enforced, even though the subsidy was claimed. Ok, so practically, that's quite an engineering challenge to achieve. Early promo vids did show Teslas being battery swapped, but it's no longer a feature. Also not unique to Tesla.
It may not be logical to restrict maintenance functions either. So there's money in trying to force everything through 'authorised' repair centres, where you can then abuse your monopoly. But then you have to provide those centres so customers get a quick turnaround. Back in the good'ol days, I could pop into a phone shop and buy a new Nokia battery & swap it myself. Now, I can't, and may have to send it off to an authorised centre. Inconvenient with a phone, more so if you have to wait 3-6 months for an 'authorised' car repair.
And Tesla battery packs might be a few thousand cells, but arranged into conveniently swappable packs, and formed from industry standard cells.. Which are produced by Panasonic. That relationship seems a little rocky, so supposing Panasonic come up with a better (or safer) 18650. Or another battery manufacturer. Why shouldn't I be able to use those in a compatible power pack? Especially if Tesla decides older packs (and cells) are obsolete & no longer supported. Or perhaps someone will come up with a conversion kit so prismatic or pouch batteries could replace Tesla's thousands of laptop cells.