I think that the letter should contain some words about the value of the software. You should thank the developer in some way, like “I found your app useful and I believe that people on F-Droid will do as well”. You should list the benefits of open-sourcing also. For companies it can be higher level of trust (it’s hard to trust closed-source software especially with dangerous permissions). For individuals(as me) publishing to F-Droid means more exposure → more translations, suggestions, bug fixes, etc → faster and easier development. It is important to tell people that publishing on F-Droid is not that hard and to offer some help during the submission process.
I believe it’s important that you clearly explain what you want and why anyone would care about. Do not assume that people know anything. Random people on the street do not know the relations between Google, Android and the Play Store, they never heard about the possibility of alternative app stores and they are clueless about the meaning of free software.
I hope we can figure out some strategies to help push this. There are a bunch of government sponsored apps in Vienna that are not free software. They are always downloadable without having to pay, so on the surface, it seems that it is a simple question to switch it to free software.
What happens is that the government contracts a company to write the apps. Those companies like to lock in customers, so they combine their own proprietary code with these apps, so that they are not 100% produced by the government funds. That means the government does not own 100% of the copyright of those apps, the apps include code licensed from the companies. So it is not a simple thing to release them as free software.
That is why free software campaigns are about doing things on “request for proposal” phase of when governments are requesting that companies bid for the contract. Then it is technically easy and little work to include a clause that requires it to be free software. The hard part is then just the political question. The established companies and relationships will not just lightly agree to it. They will say things like it’ll make the contract more expensive, since they have to rewrite the proprietary code owned by the company as free software.
What is a less exciting but easier case is making governments require unrestricted redistribution of the apps, e.g. that anyone is free to include the APKs in their own repo, etc.
Here is an example of advocating contracting policies:
-Amendment 41 Proposal for a directive Recital 37 a (new) && 42/38
…Online content sharing service providers perform an act of communication to the public and therefore are responsible for their content…
The Tagesschau app just came up on IRC. They actually have their own f-droid repo: F-Droid Repository tagesschau.de though the app itself isn’t open-source. And it contians trackers: εxodus