Everybody has different reason but what Murena does is sell phones with /e/OS pre-installed, so if one is specifically looking for a deGoogled phone because they don't have one that already supports LineageOS and/or do not know how to install LineageOS then it's very convenient. It's like going to an Apple store and leaving with a phone, not downloading a ROM then installing it on a device one already has. I'm again not saying one is better or worst than the other, solely that if one is looking for a deGoogled device and they don't have one already, it's an easier path.
PS: note also that I didn't compare /e/OS itself to LineageOS, I'm highlighting precisely how there is some value for some people.