Samsung devices have always had "OEM UNLOCKING" in the developers settings on the devices. It seems as though this feature have been taking away in the USA, but other countries still have this option available. I purchased (2) Samsung Galaxy J3 Primes (SM-J327T) and a Samsung Galaxy J7 Prime (technically called the J7 Pop (SM-J727T). Is there a reason for this and could it ever change? I never would have purchased these devices if i knew it would be a problem...
This has been brought up many times on the forum regarding Samsung locking their bootloader and some blaming T-Mobile for it. T-Mobile doesn't request it to be locked and has no issue with phones that have the bootloader unlocked, this is strictly a decision by Samsung. If and/or when they decide to unlock the bootloader again T-Mobile won't interfere or ask them to keep it locked.
So in short your answer lies with Samsung. Of course they will give you the mumbo jumbo about carriers, partnership and etc but in the end it's them.
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