Mobile SOCs are expensive, and there aren't many around that support non-android OS fully. Mobile SOC vendors aren't in the business of keeping 5 year old chips around just in case a hobby project needs some. The lower end chips don't generally come with video out features. These might all be hurdles that are solvable, but the design expertise for a decent handset isn't cheap. Other hardware vendors can get away with selling cheap phones because they will have larger scale orders and they can make money back by preloading crappy apps. A Linux phone isn't going to have huge volumes of sales, at least at first. And it's not going to sell if it's full of crapware. This issue is just way harder than it seems on the outside, even well known SBC vendors like pine64 struggle and they have a lot of SOC experience at this point. All of this is also glossing over the fact that there isn't a great Linux phone OS that is daily driver ready. I think it would be better to find something mid end that already exists and spend the effort getting the software to a better state.