Proxmox Dev here, albeit personally speaking here, so do not make more out of it than the educated opinion this is.
No, I do not think we leave much money at the table.
In short, we're targeting enterprise users with a mix of a (soft) stick (e.g. pop-up to note that one isn't having the most production ready experience) a carrot (way better tested updates and depending on the level also enterprise support).
Homelab users aren't in the target of our subscription services at all, and if we'd target them with cheap prices that would be just misused by companies too, we know this for a fact because the project is over 15 years old, and there was a lot tried out before getting to the current design.
And while there might some protection mechanisms we could set up, we rather avoid DRM'ifying Proxmox projects and avoid wasting time playing cat-and-mouse games with entities trying to abuse this.
Note though, that we still cater to the homelab in other ways even if it isn't our main target audience, like being very active on our community forums for all users, or simple having 100% FLOSS software, no open-core or other, in my opinion rather questionable, open source models.
And the price of a pop-up or using the still very stable no-subscription repository is IMO also quite small compared to the feature on gets 100% for free.
If one wants to contribute to our project but either cannot, or does not want, to afford a subscription, then I think helping out in the communities, submitting elaborate bug reports and thought out feature requests, spreading gospel at the companies they work with/for is not only cheaper for them, but also much more worth for the project.
ps. The actual license is the AGPLv3, which is always free, what we sell are subscriptions and trainings for additional services.