Why? Is there going to be a lot of alternative systems out there?
I have a 2016 (or so) phone that I bought for 70 quid 2nd hand (strictly speaking, 3rd hand, off online re-seller) and AD 2020 / 2021 it's great, really fantastic. BUT the bootloader is locked, so the phone's crippled (in many, daily, small and large but fucking annoying ways) Never mind the bye-bye to OS updates (including those "essential security ones", here's a finger - from your phone manufacturer to your phone user). Never mind the "bye-bye shitty software" hardbaked courtesy of "carefully selected business partners". If the bootloader were unlocked, as the phone is really good and those who use it are, generally, enthusiastic about it, it'd be a good incentive for people to produce mods. But locked means locked. Not that I find it strange - there's nil incentive for phone manufacturers and network providers to unlock the bootloader. In fact, there's a dis-incentive. With open bootloader, people would buy FEWER new handsets. Well, people buy fewer handsets anyway, but no business would knowingly deepen its fall. Also, there's this issue, often overlooked by the rooting enthusiasts, that unlocking a bootloader does compromise security, and promotes compromising security in general, and promotes learning how to compromise security. Many happy returns for the owners of the rooted phones, but some, sharply painful unhappy returns to those that get hacked by less scrupulous "tinkerers". Which business would want to be in the firing line for a mass lawsuit that, regardless of the result, would be costly, and cause reputational damage?
In the meantime... I think there's some drive in the EU towards making phones serviceable, and I think I heard it mentioned, some ideas to make the bootloader unlockable. That said, "ideas" v. lobbying - we know how it's going, and secondly, it might take the EU another 20 years to turn it into law, by which time the phones might have morphed into something much worse anyway...