Earlier quoted context omitted.
How much does it cost to keep everyone who wants to from gathering your personal data from that $100 phone, though?
Free if you know how to use ADB and Fastboot.
There don't seem to be any builds anywhere for the 4.1 (is it an uncommon phone?)
For argument's sake, let's say you bought the 6.1, now your option is to download an "unofficial" ROM from some pseudo-anonymous person with an anime avatar from XDA, hosted on whatever free file hosting they can find today.
Don't get me wrong, I used Lineage when it was called Cyanogenmod, and it saved one phone from landfill which is great. But I'm older now, and I need my phone to work and work well - I really don't have time for problems like https://forum.xda-developers.com/showpost.php?s=76595163ac85.... For some people, that's worth the money.
Edit: here's all the proprietary blobs that'd need to be reversed to be audited to make sure they're not selling you out, too - https://github.com/nokia-dev/proprietary_vendor_nokia/tree/a.... Props to HMD for publishing them, though.