Well, it is super simple. Not everyone is on the forums or social media.
So communities like KDE, GNOME and others started to add user feedback or info connect. This way these projects would understand on what to focus and what their users actually do. Then you have fundraisers or in-software popups to notify about donations so you may reach more people.
The issue for distributions is now that you have either to keep those implementations or modify them to redirect them to your own donation campaigns. Cos some users may say: hey I already donated to GNOME or KDE and thought you get a cut of that as well ...
If you ask companies for funding the first question is: how many users you have and how well is your product used? Can you share some numbers?
So if you have people working part-time (~ 1.800 USD/m) or full-time (~4.500 USD/m) and stack them up to around 4 - 5 people you may land around 18.000 USD/m you may need and 216.000 USD/y to even bring a realistic team on the project.
And then you may need also projects and companies using Linux in a production and want professional support and such.
However, if the user community won’t provide or even don’t want to have statistics and hardware data shared with the project you have no base-line to start for asking for partnerships and other things unless the community is willing to donate on their own in a larger scale.
Open-Source is a team effort but there is no global funding system yet. Maybe there will at some point like Sovereign Tech Fund: News | Sovereign Tech Agency