thing is that mullvad is no longer just a vpn company and expansion in other products such as search (earlier this was only for paid users) and browser (defaults to mullvad search) has caused it become what they might not want to become! remember those ram only servers and cache only for temp period? well, a server is a server and it has to store files (dumb down version) and whether stored in ram or disks, the data remains alive. mullvad now has more of such user cached data with them and this could lead to more attack surfaces. not only a user (theory) can leave behind more traces with this combination but those who are not paid users, also gonna leave huge chunk of data (including default logs/downloads/pings/updates/installs) with mullvad.
mullvad is on a strange path here and not sure if this is the "way" for it!