why not just Linux?

Choice paralysis is a real obstacle for casual users who don't have specific needs (e.g. anti-proprietary values) and don't want to know what a kernel or a binary blob is, we've even seen this with Lemmy and other Fediverse options. So giving a specific distro suggestion is effective for this, and then later enabling them to move to other distros if there's one more suited to them.

Linux Mint is generally well-received by beginner users, especially those moving from Windows which is similar enough to Cinnamon. Even if it's not the ideal distro, it's one which I believe casual users are less likely to reject. Hardware is more likely to 'just work', including graphics cards and non-free codecs. Non-free software readily appears in the app store, which is important if users are still dependent on them (e.g. their hobby group only uses Discord). While I personally believe in, support and create FOSS software, I don't see how FSF-endorsement is important to the target audience, and if it risks them complaining that their NVIDIA GPU is acting weird or they're having trouble installing proprietary tools they need for work, then I'd compromise and give them the smoothest reasonably-free option possible and allow them to decide to move to another distro later when they're more familiar with Linux and how easy it is to try out distros.