LineageOS is great, my one complaint is that it is almost never available for the phones I own. You basically have to get phones according to their popularity in a certain subgroup: for example currently one HTC model and two LG models are supported, but close to everything from OnePlus. I know I can get unofficial builds, put apart from the sometimes quite severe missing features (calling or camera not or only parti…
While popularity of phones plays some part, mostly this is down to the manufacturers. HTC are well-known for providing locked-down devices; even if you're looking for a near-stock experience, HTC tends not to be recommended. Samsung is similar in this regard, though they get away with it somewhat more than HTC due to demand. In short, don't complain to/about Lineage. Vote with your pocket and buy more open phones.
I've been using HTC devices for ages, and so far every one of them was dead-simple to unlock: Just go to the HTC developer page and enter your phone ID, get unlock code and enter on phone, done! Naturally HTC will from there on out decline responsibility for bricked phones, but which company doesn't?